Answer
Verified
423k+ views
Hint: For a function \[f\left( x \right) = a{x^2} + bx + c = 0\] the discriminant is given by \[D = {b^2} - 4ac\]. If the discriminant of the function is greater than zero the function has two real and distinct values.
Complete step-by-step answer:
Let the given function be \[f\left( x \right) = \left( {x - a} \right)\left( {x - b} \right) - 1 = 0\] which can be written as \[f\left( x \right) = {x^2} - (a + b)x + ab - 1 = 0\]
We know that for the function \[f\left( x \right) = a{x^2} + bx + c = 0\] the discriminant is given by \[D = {b^2} - 4ac\]
So, discriminant of \[f\left( x \right) = {x^2} - (a + b)x + ab - 1 = 0\] is
\[
D = {\left[ { - \left( {a + b} \right)} \right]^2} - 4(ab - 1) \\
D = {a^2} + {b^2} + 2ab - 4ab + 4 \\
D = {a^2} + {b^2} - 2ab + 4 \\
D = {\left( {a - b} \right)^2} + 4 > 0 \\
\]
Since the discriminant is greater than zero, it has two real roots.
Consider,
\[f\left( a \right) = \left( {a - a} \right)\left( {a - b} \right) - 1 = - 1\]
\[f\left( b \right) = \left( {b - a} \right)\left( {b - b} \right) - 1 = - 1\]
But \[b > a\] i.e., \[a\] and \[b\] are distinct as coefficient of \[{x^2}\] is positive (it is 1) , minima of \[f\left( x \right)\] is between \[a\] and \[b\].
Hence one root will lie in interval \[\left( { - \infty ,a} \right)\] and another root will be in interval \[\left( {b, + \infty } \right)\].
Thus, the correct option is D. one root in \[\left( { - \infty ,a} \right)\] and other in \[\left( {b, + \infty } \right)\]
Note: If the discriminant of the function is less than zero then the function has imaginary roots and if the function has discriminant equal to zero then the roots are real and equal.
Complete step-by-step answer:
Let the given function be \[f\left( x \right) = \left( {x - a} \right)\left( {x - b} \right) - 1 = 0\] which can be written as \[f\left( x \right) = {x^2} - (a + b)x + ab - 1 = 0\]
We know that for the function \[f\left( x \right) = a{x^2} + bx + c = 0\] the discriminant is given by \[D = {b^2} - 4ac\]
So, discriminant of \[f\left( x \right) = {x^2} - (a + b)x + ab - 1 = 0\] is
\[
D = {\left[ { - \left( {a + b} \right)} \right]^2} - 4(ab - 1) \\
D = {a^2} + {b^2} + 2ab - 4ab + 4 \\
D = {a^2} + {b^2} - 2ab + 4 \\
D = {\left( {a - b} \right)^2} + 4 > 0 \\
\]
Since the discriminant is greater than zero, it has two real roots.
Consider,
\[f\left( a \right) = \left( {a - a} \right)\left( {a - b} \right) - 1 = - 1\]
\[f\left( b \right) = \left( {b - a} \right)\left( {b - b} \right) - 1 = - 1\]
But \[b > a\] i.e., \[a\] and \[b\] are distinct as coefficient of \[{x^2}\] is positive (it is 1) , minima of \[f\left( x \right)\] is between \[a\] and \[b\].
Hence one root will lie in interval \[\left( { - \infty ,a} \right)\] and another root will be in interval \[\left( {b, + \infty } \right)\].
Thus, the correct option is D. one root in \[\left( { - \infty ,a} \right)\] and other in \[\left( {b, + \infty } \right)\]
Note: If the discriminant of the function is less than zero then the function has imaginary roots and if the function has discriminant equal to zero then the roots are real and equal.
Recently Updated Pages
Assertion The resistivity of a semiconductor increases class 13 physics CBSE
The Equation xxx + 2 is Satisfied when x is Equal to Class 10 Maths
How do you arrange NH4 + BF3 H2O C2H2 in increasing class 11 chemistry CBSE
Is H mCT and q mCT the same thing If so which is more class 11 chemistry CBSE
What are the possible quantum number for the last outermost class 11 chemistry CBSE
Is C2 paramagnetic or diamagnetic class 11 chemistry CBSE
Trending doubts
State the differences between manure and fertilize class 8 biology CBSE
Why are xylem and phloem called complex tissues aBoth class 11 biology CBSE
Difference between Prokaryotic cell and Eukaryotic class 11 biology CBSE
Difference Between Plant Cell and Animal Cell
What would happen if plasma membrane ruptures or breaks class 11 biology CBSE
Give 10 examples for herbs , shrubs , climbers , creepers
What precautions do you take while observing the nucleus class 11 biology CBSE
What would happen to the life of a cell if there was class 11 biology CBSE
Change the following sentences into negative and interrogative class 10 english CBSE