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Access NCERT Exemplar Solutions for Grade 12 Mathematics Chapter 6.- Application of Derivatives
Solved Examples
Short Answer Type (S.A.)
1. For the curve y =5x-2x3 if x increases at the rate of 2 units/sec, then how fast is the slope of curve changing when x = 3?
Ans: Here x is increasing at the rate of 2unit/sec, so we can write this as
Now we find the slope of the curve which is
We have asked to find the change in slope which can we written mathematically as:
-sign represents that slope is decreasing. Hence the slope will decrease at the rate of 72unit/sec.
2. Water is dripping out from a conical funnel of semi-vertical angle
Ans:

Given-
and
We know that the surface area of cone is
Now we reform this relation in terms of s and
So,
Now,
When
3. Find the angle of intersection of the curves
Ans: First we find the intersection points of the given curve and then find the angle between the slope of curves on the intersection points. So first we solve both the equations:
From eq. 1 and 2
Now slope of tangent on curve
and slope of tangent on curve
At (0,0) slope of
Hence angle of intersection at point (0,0) =
At point (1,1) slope of tangent on curve
Angle b/w two lines
4. Prove that the function f(x) = tanx – 4x is strictly decreasing on
Ans: We know that a function is strictly decreasing if f′(x)<0 in the given interval.
Given:
Here f′(x)=
For given interval
Thus for
5. Determine for which values of x, the function
Ans: Here we first find the derivative of the given function as:
Now we put this value equal to 0 for finding the critical points such as:

Since f’(x) is continuous in the interval
6. Show that the function
Ans:
For critical point
Here at
7. Using differentials, find the approximate value of
Ans: Let
We know that,
Here we write 0.082 as = 0.09-0.008 =
8. Find the condition for the curves
Ans: For the curves becoming orthogonal the slope of tangents on the curves should be perpendicular like
Let the curves intersect at point(h,k). So now we find the slope of tangents on both the curves,
Now using the curve
For orthogonality the condition is
9. Find all the points of local maxima and local minima of the function
Ans:
Now we find the critical points as
For Finding maxima and minima we find the second derivative as:
On substituting x=0,-5,-3 in f’’(x) the function will have local maxima if f’’(x)
<0 and will have local minima if f’’(x)>0.
10. Show that the local maximum value of
Ans: Given
For finding the local maxima and minima we first find out the first derivative, after solving the f’(x) we get critical points and for those critical points we check the second derivative of the function whether it is negative or positive.
Now,
Hence Local maximum value(-2) is less than local minimum value(2).
Long Answer Type (L.A.)
11. Water is dripping out at a steady rate of 1 cu cm/sec through a tiny hole at the vertex of the conical vessel, whose axis is vertical. When the slant height of water in the vessel is 4 cm, find the rate of decrease of slant height, where the vertical angle of the conical vessel is
Ans:

Here we are given that the water is dripping out that means =
We know that volume of a cone
From the figure:
Putting the values of r & h in eq. 1
Therefore, the rate of decrease of slant height is
12. Find the equation of all the tangents to the curve
Ans:
Given:
This is the slope of the tangent to the given curve.
Now we have a line
Since we equate the slopes of line and tangent as:
After squaring on both side in eq. 1 and eq.2 and adding them
Now putting this value in eq.2
Given that
Hence the points are
Now the equation of tangent passing through the point
13. Find the angle of intersection of the curves
Ans: Given
The angle of intersection of the curve means the angle between the tangents on both curves. First we find the intersection point for both the curves.
Substituting these values in
And
At (0,0) the slope of tangent to the curve
At
And the slope of tangent to the curve
Therefore the angle b/w the curve is
14. Show that the equation of normal at any point on the curve
Ans:
Now,
Now we find the slope as
The equation of line passing through a point
We know that
Hence the equation of normal on the curve is
15. Find the maximum and minimum values of
Ans: Here for finding the maxima and minima, first we find the critical points.
Now for critical points,
Here on putting
Here we get the maxima when f’’(x)<0 and minima when f’’(x)<0.
At x=
At x=
At x=
Therefore function has minima at x=
SO from the above the maxima points are 0,
Now the maximum values of f(x) is f(0)=
f(
Minimum value at
16. Find the area of the greatest rectangle that can be inscribed in an ellipse

Ans: From the figure,
Let the side on the major axis is =2x, side on the minor axis = 2y. Now the area of rectangle
Now we have to maximise this function for getting the maximum area of a rectangle.
For critical points
On putting the value
Now,
At
Hence At
Maximum area
17. Find the difference between the greatest and least values of the function
Ans:
For critical points
Now in interval
If we compare all four value the greatest value is
.18. An isosceles triangle of vertical angle 2θ is inscribed in a circle of radius a. Show that the area of triangle is maximum when

Ans: Given ABC is an isolated triangle.
We know that area of triangle =
Here Height = AD, Base = BC
BC=2BD=
AD=OA+OD where OA =Radius =a and OD=OB
Hence AD=
Now Area of triangle
We have to maximise this area of triangle where the area depends on angle
For critical points
At
Objective Type Questions
Choose the correct answer from the given four options in each of the following Examples 19 to 23.
19. The abscissa of the point on the curve
(A) 1
(B)
(C) 2
(D)
Ans: Given:
Let the point on the curve is
So the curve is
Now we find the Slope of normal at this point.
Slope of Normal =
Equation of normal Passing through origin
Now the Equation of normal on point
By using eq. 1 & 2
Let
20.The two curves
(A) touch each other
(B) cut at right angle
(C) cut at an angle
(D) cut at an angle
Ans: First we find the slope of both the curves.
Differentiating on both sides
Differentiating on both sides
By Eq. 1 & 2 We can write
21. The tangent to the curve given by
(A) 0
(B)
(C)
(D)
Ans: Slope of the tangent of the curve is
Slope at point
Hence the tangent (y-axis) will make angle
22. The equation of the normal to the curve y = sinx at (0, 0) is:
(A)
(B)
(C)
(D)
Ans: Slope of the tangent =
Slope of the Normal =
Slope of the Normal =
Equation of normal having slope -1, passing through (0,0) is
Hence option c is the correct answer.
23. The point on the curve
(A)
(B)
(C) (4, 2)
(D) (1, 1)
Ans: Given:
Slope of the tangent of curve
So on differentiating the given curve
Let the point on curve is
On Putting this value in curve equation we get
Hence the point is
24. The values of a for which
Ans: The curve touches the x-axis that means the tangent on the curve will touch the x-axis. So we first find the slope and equate it with 0.
Therefore,
Now on putting
Hence the values of a are
25. If
Ans: For the function
Let
For critical points
Since
Hence
26. Let f have a second derivative at c such that
Ans: We know that if we have a function f such that at c,
27. Minimum value of f if
Ans: We know that sin function
Given:
For critical points
At
At
Hence
28. The maximum value of sinx + cosx is _____.
Ans: Let
For critical points,
At
29. The rate of change of volume of a sphere with respect to its surface area, when the radius is 2 cm, is______.
Ans: Volume of a sphere is V=
Here the rate of change of volume w.r.t surface will be =
S=
Using the values from Eq.(2)&(3) in Eq.(1)
When r=2
EXERCISE
Short Answer (S.A.)
1. A spherical ball of salt is dissolving in water in such a manner that the rate of decrease of the volume at any instant is proportional to the surface. Prove that the radius is decreasing at a constant rate.
Ans: Given that the rate of decrease of the volume at any instant is proportional to the surface . Let the radius of the spherical ball is r.
Volume of sphere V=
Surface area of sphere
According to the problem
Since
2. If the area of a circle increases at a uniform rate, then prove that perimeter varies inversely as the radius.
Ans: Given that the area of the circle is increasing at a uniform rate as
Let the radius of a circle =r
Area of a circle
By Eq. 1 & 2
Let the perimeter
Putting the values of
Hence the perimeter varies inversely as the radius.
3. A kite is moving horizontally at a height of 151.5 meters. If the speed of the kite is 10 m/s, how fast is the string being let out; when the kite is 250 m away from the boy who is flying the kite? The height of the boy is 1.5 m.
Ans:

Height(h)=151.5m, Speed of kite =10m/s
From the figure, Let CD be the height of the kite and AB is the height of the boy.
Let
Using pythagoras theorem in
Here AC=250m , AE= x , EC=150m
When
Now ,
Differentiating on both sides
On putting the values x=20, y=250 and
So, the string being let out at the rate of
4. Two men A and B start with velocities v at the same time from the junction of two roads inclined at 45° to each other. If they travel by different roads, find the rate at which they are being seperated.
Ans:

Let the men A and B start from point c with the
Same velocities v at the same time.
And given,
Since, Men A and B moving with same velocities v at the same time , so they will cover the same distance,
Hence AC=AB, Therefore the triangle ABC is an isosceles triangle.
Now we draw
Let at time t the distance b/w A and B is y and AC=x
In
By ASA ,
Since,
In
Since distance b/w A and B is y. Hence the rate of the separation of A and B is
Differentiating the equation 1 w.r.t. t,
So the rate is
5. Find an angle θ,
Ans: Let the angle
Now,on differentiatingboth sides w.r.t. t, we get
So the required angle is
6. Find the approximate value of
Ans: Let
We write 1.999 as
Let x=2 then
Differentiating on both sides w.r.t. T, we get
Now
7. Find the approximate volume of metal in a hollow spherical shell whose internal and external radii are 3 cm and 3.0005 cm, respectively.
Ans: Let the external radius of spherical shell
Volume of hollow spherical shell
We can find the value of
Let
Also let
Now we differentiate on both sides w.r.t. t,
So now
Since
8. A man, 2m tall, walks at the rate of
Ans:

From the figure, Let AB be the height of street light source and CD be the height of man, CD=2m.
Let
From
On differentiating both sides w.r.t. T
Let the distance of tip of shadow from the foot of street light post is Z
Now on differentiating both sides w.r.t. T, we get
Therefore the tip of shadow is moving at the rate of
9. A swimming pool is to be drained for cleaning. If L represents the number of litres of water in the pool t seconds after the pool has been plugged off to drain and
Ans: Given that L represents the number of liters of water in the pool t seconds after the pool has been plugged off to drain and that is
Let the rate at which water is running out =
Rate at which the water is running out at the t=5s
Since the initial Rate =
Now the average rate =
10. The volume of a cube increases at a constant rate. Prove that the increase in its surface area varies inversely as the length of the side.
Ans: Let the Side of a cube = x
We know the volume of a cube
Differentiating on both sides w.r.t. t,
Also the surface area of cube
Differentiating on both sides w.r.t. t,
Now by putting the value of
Hence the increase in its surface area varies inversely as the length of the side.
11. x and y are the sides of two squares such that
Ans: Given : x and y are the sides of two squares such that
Let the area of first square having side x is
The area of second square having side y is
Now,
Differentiating on both sides w.r.t. t,
And
Differentiating on both sides w.r.t. t,
Dividing Eq. 2 by Eq. 1
12. Find the condition that the curves
Ans: Here first we find the point of intersection of given curves.
Now putting this value in eq. 1
Now substituting this value in
Thus the point of intersection of curves is
Orthogonality means the tangents on both the curves are intersecting each other at an angle of
Differentiating on both sides w.r.t. x,
Differentiating on both sides w.r.t. X,
Since curves intersect orthogonally, So
Hence for intersecting the given curve orthogonally the required condition is
13. Prove that the curves xy = 4 and
Ans: If the curves touch each other then the slope of tangents on both curves on the touching point are the same . Since we have to prove this condition.
So first we find the touching point.
Let we have a point (x,y) where the curves intersect.
xy = 4
Now on putting the value of
Let
Now from Eq. 1
So the touching points (2,2) & (-2,-2)
Now we find the slopes of both curves:
xy = 4
On differentiating both sides w.r.t. x,
Also,
Differentiating on both sides w.r.t. x,
For point (2,2)
Also for point (-2,-2)
Thus, for both the intersection points,We see that the slopes of both curves are the same. Hence, the curves touch each other.
14. Find the coordinates of the point on the curve
Ans: Given that we have a curve
Differentiating on both sides w.r.t. x,
The tangent inclined equally on both axes hence
Squaring on both sides we get
From eq. 1 ,
Putting this value in eq. 2
Hence the required coordinates of the point are (4,4).
15. Find the angle of intersection of the curves
Ans: Given that both curves are intersecting each other so first we find the intersection point and then find the angle b/w the tangents on both curves drawn on intersecting points.
From Eq. 1 & 2
Now from eq. 1
So the intersection points are
Now we find the slopes of both curves
For point
So for point
Now for point
Here
Therefore, For both intersecting points we get the angle
16. Prove that the curves
Ans: If the given curves touch each other then the slope of tangents on both curves at the intersecting point is same.
Let the slope of curve
Differentiating on both sides w.r.t. x,
And
Differentiating on both sides w.r.t. x,
Thus we see that the slope of both the curves are equal toeach other i.e.,
17. Find the equation of the normal lines to the curve
Ans: We are given an equation of a curve
First we find the slope of normal on the given curve
Differentiating on both sides w.r.t. X
This is the slope of tangent on the given curve but we have to find the slope of normal, and we know that
It is given that the normal is parallel to the line x + 3y = 4. We know that the slope of two parallel lines are the same hence the slope of normal will be equal to the slope of the given line . So the slope of line
On substituting
For x=2, from eq. 2
For x=-2, y=-2
Hence the (2,2) and (-2,2) are the points where the normal at the given curve is parallel to line x + 3y = 4.
Now the Required equations of normals passing through points (2,2) & (-2,2) and having slope of
So the required equations of Normal are
18. At what points on the curve
Ans: We are given an equation of the curve
Differentiating on both sides w.r.t. x,
This is the slope of tangent which is parallel to y-axis and we know that the slope of y-axis is
On substituting
Hence the required points are (3,2) &(-1,2) where the tangents are parallel to the y-axis.
19. Show that the line
Ans: Given we have given a curve
We know that if two curves touch each other at a point then the slope of both the curves at the meeting point should be equal i.e.
are slopes of curves.
The curve
So the point of intersection is (0,b).
Now the slope of curve at point (0,b) is:
Also slope of the line
Differentiating the equation of line w.r.t. x,
From eq. 1 and eq.2
Therefore, the line
20. Show that
Ans: Given function
A function is said to be increasing function if
Differentiating the function w.r.t. x,
For increasing function,
This is true for every value of x, Hence the f(x) is increasing in R.
21. Show that for a ≥ 1,
Ans: We have function
We know that a function is said to be decreasing if
Differentiating the function w.r.t. x,
We know that
Here we have to prove that the function is decreasing , we know that the function is decreasing if
So ,
Therefore the function will be decreasing for
22. Show that
Ans: The given function
Differentiating the function
For increasing function
This is true when
So the function is increasing in
23. At what point, the slope of the curve
Ans: The curve we have:
Slope of tangent on the curve
Now,
For critical point,
For slope to be maximum,
Now ,
On substituting x=1 in eq. 1 we get,
So the point is (1, -16) at which the slope of the curve is maximum .
Slope at x=1,
Hence the point is (1, -16) and the maximum slope is 12.
24. Prove that
Ans:
The function we have :
Differentiating the function w.r.t. X,
For critical point
For finding either function has maxima or minima, we again differentiate the
At
Thus the function has local maxima and the point of maxima is
25. If the sum of the lengths of the hypotenuse and a side of a right angled triangle is given, show that the area of the triangle is maximum when the angle between them is
Ans:

Let the triangle is
AB=x, AC=h
Given :
By using the pythagorean theorem in triangle
By eq. 1
Now area of triangle
Now we have to maximize the area of the triangle, So we differentiate w.r.t. x,
For critical points,
Again differentiating
At
So area will be maximum at
On putting the value
So the point is
Therefore the area of triangle is maximum when the angle is
26. Find the points of local maxima, local minima and the points of inflection of the function
Ans: Given function
Differentiating the function w.r.t. x,
For critical points
(Image will be uploaded soon)
If we see at point x=0 , the value of f’(x) is not changing that means the function has neither maxima nor minima.
At x=1, the value of f’(x) is changing from +ve to -ve so at x=1 the function has local maxima.
So the corresponding maximum value is
At x=3 , the value of f’(x) is changing from -ve to +ve so at x=3 the function has local minima.
Now the corresponding minimum value is
27. A telephone company in a town has 500 subscribers on its list and collects fixed charges of Rs 300/- per subscriber per year. The company proposes to increase the annual subscription and it is believed that for every increase of Re 1/- one subscriber will discontinue the service. Find what increase will bring maximum profit?
Ans: Let the company increase its annual subscription by x Rs.
So the x subscriber will discontinue the service.
Now the total revenue of the company after the increment
On differentiating both sides w.r.t. x,
Now,
For finding maxima and minima of the function we again differentiate
So the revenue will be maximum at x=100.
Hence the maximum value of revenue
Hence the company will earn the maximum profit at the increment of 100 Rs.
28. If the straight line x cosα + y sinα = p touches the curve
Ans: Given curve
It is given that the line x cosα + y sinα = p touches the curve that means the slope of the line should be equal to the slope of the tangent to the curve.
On differentiating both sides w.r.t. x,
This slope should be equal to the slope of line x cosα + y sinα = p which is
Now,
Let
So the point is
On substituting the point in given curve, we get
Now substituting the point
Squaring on both sides
Now on dividing eq.(3) by eq.(2)
29. An open box with square base is to be made of a given quantity of card board of area
Ans:

Let the side of the square base is x and its height is y.
Area of base =
Given: The area of the metal used is
Volume of the box
On substituting the value of y from eq.1, we get
Now on differentiating w.r.t. x, we get
Now,
Here x represents the side of the box , Hence we reject
Hence
Again, differentiating Eq.(ii) w.r.t. X, we get
Therefore we get the maximum value at
So the maximum volume
30. Find the dimensions of the rectangle of perimeter 36 cm which will sweep out a volume as large as possible, when revolved about one of its sides. Also find the maximum volume.
Ans:

Let the breadth and length of the rectangle
be x and y respectively.
∵ Perimeter of rectangle
Given perimeter P=36cm
So,
Now according to the problem, let the rectangle be revolved out about its length y , then the new shape cylinder is formed.
The volume of the cylinder is
On substituting
On differentiating w.r.t. x, we get
Now
Here x represents the side of a rectangle and we know that side can’t be 0.
So, x=0(rejected)
Again, On differentiating
At x=12,
Hence at x=12, Cylinder has maximum volume.
Therefore the volume at x=12,
.31. If the sum of the surface areas of a cube and a sphere is constant, what is the ratio of an edge of the cube to the diameter of the sphere, when the sum of their volumes is minimum?
Ans: Let the side of a cube is x and radius of sphere is r.
Surface area of cube =
Surface area of sphere
And,
Now, the volume of cube
Volume of sphere =
Le the sum of their volume is
For critical points,
re r represents the radius and radius can’t be zero.
Hence
∴
On differentiating again
Hence the sum of their volumes at
At
Now the ratio of edge of cube to the diameter of sphere is =
Hence the ratio of edge of cube to the diameter of sphere is
32. AB is the diameter of a circle and C is any point on the circle. Show that the area of

Ans:
Let the sides of the triangle is
We have to prove that the area of the triangle is maximum and the triangle is isosceles means (x=y).
We have
Now, Area of triangle
Now,differentiating both sides w.r.t. x, we get
For critical point,
Here x represents the side of the triangle and the side can’t be negative. So
For finding whether the area of triangle is maximum and minimum we again differentiate
At
Hence at
For
If we see, here
33. A metal box with a square base and vertical sides is to contain
Ans:

Let the side of the base be x and height is y.
Volume of the box
So,
The cost for bottom and top =
So the total cost is denoted as
substituting the value of y from eq. 1
On differentiating w.r.t. x,
Now,
Again, differentiating
Hence the cost at
The cost at
34. The sum of the surface areas of a rectangular parallelopiped with sides x, 2x and
Ans: Given that we have the sides of a rectangular parallelopiped as
Let the sum of surface area is S
Volume of parallelopiped =
Volume of sphere =
Let the Sum of the volume of parallelopiped and volume of the sphere is V.
Then,
On differentiating w.r.t. x, we get
Now,
Again differentiating
At
For
From eq. 1 , for
Hence x is 3 times the radius of the sphere.
Now the minimum sum of volume is
Choose the correct answer from the given four options in each of the following questions 35 to 39:
35. The sides of an equilateral triangle are increasing at the rate of 2 cm/sec. The rate at which the area increases, when side is 10 cm is:
Ans: Let the side of the equilateral triangle is
Area of equilateral triangle
Given that
On differentiating the eq.(1). W.r.t. t, we get
When
Hence the area is increasing at the rate of
36. A ladder, 5 meter long, standing on a horizontal floor, leans against a vertical wall. If the top of the ladder slides downwards at the rate of 10 cm/sec, then the rate at which the angle between the floor and the ladder is decreasing when lower end of ladder is 2 metres from the wall is:
Ans:

Let the angle b/w floor and the ladder is
And sides of the triangle are
From the figure,
Given that the top of the ladder slides downwards at the rate of 10cm/sec.
Hence
Differentiating on both sides w.r.t. T, we get
On substituting the value of
Given that lower end from the wall is 2m=200cm
Hence,
Therefore option B is the correct answer.
37. The curve
(A) a vertical tangent (parallel to y-axis)
(B) a horizontal tangent (parallel to x-axis)
(C) an oblique tangent
(D) no tangent
Ans: The curve we have
Now the slope of the tangent on the curve is
Slope on point (0,0) is
Here slope of the tangent is
38. The equation of normal to the curve
(A) 3x – y = 8
(B) 3x + y + 8 = 0
(C) x + 3y ± 8 = 0
(D) x + 3y = 0
Ans: The given curve we have
On comparison with equation
Now,
On differentiating w.r.t. x , we get
Now, Slope of the normal to the curve
On substituting this value in the given equation of thecurve, we get
For
For
So the points are (2,2) &(-2,-2) at which normal is parallel to line x + 3y = 8 .
Now the equation of normals passing through points (2,2) &(-2,-2) and having slope
Hence the equation of normals is
39. If the curve
(A). 1
(B). 0
(C). – 6
(D). 6
Ans: Given that the curves cut orthogonally at point (1,1) that means the slope of both the curves should satisfy the condition
Differentiating on both sides w.r.t. x, we get
Now,
Differentiating on both sides w.r.t. x,
Given that both curves cut orthogonally. So,
Therefore the correct option is D.
40. If
(A) 0.32
(B) 0.032
(C) 5.68
(D) 5.968
Ans: We have the curve
We know that
Now,
On differentiating on both sides w.r.t. x, we get
Changes in x is
Now,
Hence option A is the correct answer.
41. The equation of tangent to the curve
(A) x + 5y = 2
(B) x – 5y = 2
(C) 5x – y = 2
(D) 5x + y = 2
Ans: Given curve
The curve passes crosses the x-axis, hence
Hence the point where the tangent passes through is (2,0).
Now, we find the slope of the tangent on curve
On differentiating both sides w.r.t. x, we get
Slope at the point (2,0)
Now the equation of tangent passing through (2,0) and having slope
Hence the correct option is option A.
42. The points at which the tangents to the curve
(A) (2, –2), (–2, –34)
(B) (2, 34), (–2, 0)
(C) (0, 34), (–2, 0)
(D) (2, 2), (–2, 34)
Ans: The given curve is
For finding the slope of tangent on the curve we differentiate the given equation of curve w.r.t. x,
Given that the tangent is parallel to the x-axis, so the above slope will be equal to 0 as we know that the slope of the x-axis is 0 and if two lines are parallel then their slopes are to be equal. Therefore,
For
For
Hence the required points are (2,2) and (-2,34) where the tangents to the curve
43. The tangent to the curve
(A) (0, 1)
(B)
(C) (2, 0)
(D) (0, 2)
Ans: The given curve we have
Slope of tangent to the curve is
Slope at point
Now, the equation of a tangent passing through the point (0,1) and having slope 2 is:
It is asked that the tangent meets x-axis , so on substituting y=0 in equation of tangent, we get
Thus the point where tangent meets the x-axis is
44. The slope of tangent to the curve
(A)
(B)
(C)
(D) – 6
Ans: The equation of curve we have
Differentiating w.r.t. t,
We know that the slope is
So
Given that the curve passes through the point (2, –1) , So
Here the common value of t is 2.
Now at t=2 the slope of tangent is
Therefore the slope of tangent to the curve is
45. The two curves
(A)
(B)
(C)
(D)
Ans: The equations of curves we have
On Differentiating the first curve w.r.t. x, we get
Now On differentiating the second curve
If we see
We know that if
46. The interval on which the function
(A) [–1, ∞ )
(B) [–2, –1]
(C) (– ∞ , –2]
(D) [–1, 1]
Ans: We have the function
We know that a function is said to be decreasing if
So on drawing the points on number line

We see that
47. Let the f : R → R be defined by
(A) has a minimum at x = π
(B) has a maximum, at x = 0
(C) is a decreasing function
(D) is an increasing function
Ans: The given function is
Differentiating the function w.r.t. x,
We know that
So,
Since
Hence the function is an increasing function. Option D is the correct answer.
48.
(A) 1 < x < 3
(B) x < 0
(C) x > 0
(D)
Ans: The given function is
Differentiating the given function w.r.t. x,
We know that the function is decreasing function if

So the function decreases for
49. The function
(A) increasing in
(B) decreasing in
(C) decreasing in
(D) decreasing in
Ans: The given function is
Differentiating the given function w.r.t. x,
We know that
Hence
So the function is decreasing function in
50. Which of the following functions is decreasing on
(A) sin2x
(B) tanx
(C) cosx
(D) cos 3x
Ans: We know that a function is said to be decreasing function if
So
Differentiating the function w.r.t. x,
Hence option C is the correct answer.
51. The function
(A) always increases
(B) always decreases
(C) never increases
(D) sometimes increases and sometimes decreases.
Ans: The given function is
Differentiating the function w.r.t. x,
Hence
52. If x is real, the minimum value of
(A) –1
(B) 0
(C) 1
(D) 2
Ans: The given function is
Differentiating the function w.r.t. x,
For critical point
We know that a function has local minima if f’’(x)>0.
So here we have to find the 2nd derivative of the given function.
Hence we get the minimum value at x=4.
Now the value of function at x=4 is the minimum value of the function.
Hence the option c is the correct answer.
53. The smallest value of the polynomial
(A) 126
(B) 0
(C) 135
(D) 160
Ans: The given polynomial function is
Differentiating the function w.r.t. x,
So,
Now we find the value of given function at points x=0,4,8,9
If we see the minimum absolute value of the function is 0 in [0,9]. Hence the correct option is option B.
54. The function
(A) two points of local maximum
(B) two points of local minimum
(C) one maxima and one minima
(D) no maxima or minima
Ans: The given function is
Differentiating the function w.r.t. x,
For critical points
Differentiate again
At x=-1,
At x=2,
Since the function has one maxima and one minima. So the option C is the correct answer.
55. The maximum value of sin x . cos x is
(A)
(B)
(C)
(D)
Ans: We have the function
Differentiating the function w.r.t. x,
Now,
Again differentiating
The value of the function at
56. At
(A) maximum
(B) minimum
(C) zero
(D) neither maximum nor minimum.
Ans: The function we have, is
Differentiating the function w.r.t. x,
For finding, the function has minima or maxima at
Now,
At
57. Maximum slope of the curve
(A) 0
(B) 12
(C) 16
(D) 32
Ans: The curve we have,
Slope of the curve =
Now we find whether the slope of the curve is maximum or minimum.
Differentiating the slope of the curve w.r.t. X,
For critical points,
Now,
So the slope of curve at
Therefore the correct answer is option B.
58.
(A)
(B)
(C)
(D)
Ans: The function we have,
Let
Taking log on both sides
Differentiating on both sides w.r.t. x,
For the stationary points
This is the stationary point. So option B is the correct answer.
59. The maximum value of
(A) e
(B)
(C)
(D)
Ans: The function we have,
Let
Taking log on both sides
Differentiating on both sides w.r.t. x,
For critical points,
Again differentiating
Now,
Hence the function has maxima at
So the maximum value of function at
Therefore option C is the correct answer.
Fill in the blanks in each of the following Exercises 60 to 64:
60. The curves
Ans: The given curves are
Given that the curves touch each other so the slope of both the curves should be the same.
For slope of curves, differentiate both curves w.r.t. x,
Differentiating w.r.t. x,
Also,
Differentiating w.r.t. X,
Now equating the slopes from eq.1 and eq.2
For
For
So the required points are
61. The equation of normal to the curve
Ans: The given curve is
Differentiating the curve w.r.t. x,
Now the slope of the curve at (0,0)
Slope of Normal=
The equation of normal passing through (0,0) and having slope -1
So the equation of normal to the curve
62. The values of a for which the function
Ans: The given function is
Differentiating the function w.r.t. x,
We know that a function is increasing function if
Given that the function is increasing in R.
Hence
Since
For the condition
So the values of a should be
63. The function
Ans: The given function is
Differentiating the function w.r.t. x,
A function is decreasing function if
So the function decreases in interval
64. The least value of the function
Ans: The given function is
Differentiating the function w.r.t x,
For critical points,
Since given that x>0, hence
Now again differentiating
At
Since a>0 and b>0 , Hence
Now the minimum value at
Therefore the least value is
Chapter 12 - Application of Derivatives
Chapter 12 - Application of Derivatives is an important Chapter for the boards of Class 12th. The Exemplar will help students to solve the questions and strengthen important concepts and will act as a revision. Students will learn the concept of rate of change of quantitative, tangents and normal approximation, increasing and decreasing functions, maximum and minimum values of functions in closed intervals, and maxima and minima through Chapter 6. Students focusing on the strong grip on the Chapter can reach out the Vedantu’s official site and go for the exemplar for the respective Chapter.
Vedantu also offers other online material for Chapter 6 - Application of Derivatives like notes, sample question papers, additional questions, and last year’s papers. The notes offered by the Vedantu are designed by their expert faculty for the students to understand the theoretical concepts of the Chapter. A good collection of sample papers and additional questions are also offered that will give an upper hand to students for the practice during the preparation. The PDF also consists of last year’s paper so that the students can know what type of questions are asked in the Exam. Vedantu also offers live sessions for the students, so that they can revise the topics they have learned and clear doubts from the teachers. The teaching faculty of Vedantu is a group that focuses on enhancing the results for the registered students.
FAQs on NCERT Exemplar for Class 12 Maths - Application Of Derivatives - Free PDF Download
1. From where do students download the exemplar for the Chapter 6 Application of Derivatives?
Students can easily visit Vedantu’s official website and can find the exemplar PDF for the Chapter 6 Application of Derivatives. The NCERT for the Chapter 6 Application of Derivatives exemplar is available in PDF form. The PDF is designed as per the latest syllabus advised by the Central Board of Secondary Education. The PDF is designed by the expert faculty of Vedantu as per the latest syllabus students following the Exemplar will have an upper hand because of the content mentioned in the PDF.
2. How is Vedantu beneficial for the students in their studies?
Vedantu is very beneficial when it comes to studying as Vedantu offers online material like notes, sample question papers, additional questions, and last year’s papers. A good collection of sample papers and additional questions are also offered that will give an upper hand to students for the practice during the preparation. The notes offered by the Vedantu are designed by the expert faculty of Vedantu for the students to understand the theoretical concepts of the respective Chapter.
3. Is Chapter 6 Application of Derivatives important for Class 12?
Chapter 6 Application of Derivatives is very important for Class 12 as the Chapter consists of many important topics and concepts that are surely asked in the Exams. Students will learn the concept of rate of change of quantitative, tangents and normal approximation, increasing and decreasing functions, maximum and minimum values of functions in closed intervals, and maxima and minima.
4. How is the Exemplar of Chapter 6 Application of Derivatives?
The Exemplar for the Chapter 6 Application of Derivatives is designed as per the latest syllabus advised by the Central Board of Secondary Education. The Exemplar is designed by the expert faculty of Vedantu itself. The Exemplar consists of many important topics that are constantly asked in different ways. The topics have additional questions that can be used for practice in the preparation period.

















