# If \[\;y = y(x)\] is the solution of the differential equation \[\,\left( {\dfrac{{2 + \sin x}}{{y + 1}}} \right)\dfrac{{dy}}{{dx}} + \cos x = 0\].

With \[y(0) = 1\] then \[y(\dfrac{\pi} {2} )\;\_\_\].

Last updated date: 19th Mar 2023

•

Total views: 306.6k

•

Views today: 6.85k

Answer

Verified

306.6k+ views

Hint: Separate dy and dx then integrate the equation. We use the variable separable method.

Given :-

\[\left( {\dfrac{{2 + \sin x}}{{y + 1}}} \right)\dfrac{{dy}}{{dx}} + \cos x = 0\]

After transposing we get,

\[\left( {\dfrac{1}{{y + 1}}} \right)dy = - \left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx\]

On integrating we get,

\[\int {\left( {\dfrac{1}{{y + 1}}} \right)dy = - \int {\left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx} } \,\,\,...({\text{i}})\]

First we will solve this,

\[\int {\left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx} \]

Let \[\sin x = t\]

Then \[\cos xdx = dt\]

From the above two equations the integral becomes,

\[\int {\left( {\dfrac{1}{{2 + t}}} \right)dt = \ln (2 + t)} \,\, + \ln {c_1}\]

On putting the value of \[{\text{ }}t\],

\[\log (2 + t) = \log (2 + \sin x)\]

On putting these values in equation (i), we get equation (i) as ,

\[\ln (y + 1) = - \ln (2 + \sin x) + \ln c\]

Then we got an equation as,

\[y = \dfrac{c}{{2 + \sin x}}\, - 1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,......(\ln a - \ln b = \ln \dfrac{a}{b})\]

From the question,

\[y(0) = 1\]

So,

\[

{\text{1 = }}\dfrac{c}{{2 + 0}} - 1\,\,\,\,\,\,\,\,\,\,\,......(\sin 0 = 0) \\

c = 4 \\

\]

The equation is ,

\[y = \dfrac{4}{{2 + \sin x}}\, - 1\,\,\,\]

We have asked to find \[y\left( {\dfrac{\pi }{2}} \right)\],

So,

\[y\left( {\dfrac{\pi }{2}} \right) = \,\dfrac{4}{{2 + 1}}\, - 1 = \dfrac{1}{3}\,\,\,\,\,\,\,\,\,......(\sin \left( {\dfrac{\pi }{2}} \right) = 1)\]

Hence the correct option is A.

Note: In these types of questions first open the integral by variable separation method then when the equation is obtained, get the value of constant from the information provided in the question then after getting completely , get the answer which is asked in question by putting the value of constant.

Given :-

\[\left( {\dfrac{{2 + \sin x}}{{y + 1}}} \right)\dfrac{{dy}}{{dx}} + \cos x = 0\]

After transposing we get,

\[\left( {\dfrac{1}{{y + 1}}} \right)dy = - \left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx\]

On integrating we get,

\[\int {\left( {\dfrac{1}{{y + 1}}} \right)dy = - \int {\left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx} } \,\,\,...({\text{i}})\]

First we will solve this,

\[\int {\left( {\dfrac{{\cos x}}{{2 + \sin x}}} \right)dx} \]

Let \[\sin x = t\]

Then \[\cos xdx = dt\]

From the above two equations the integral becomes,

\[\int {\left( {\dfrac{1}{{2 + t}}} \right)dt = \ln (2 + t)} \,\, + \ln {c_1}\]

On putting the value of \[{\text{ }}t\],

\[\log (2 + t) = \log (2 + \sin x)\]

On putting these values in equation (i), we get equation (i) as ,

\[\ln (y + 1) = - \ln (2 + \sin x) + \ln c\]

Then we got an equation as,

\[y = \dfrac{c}{{2 + \sin x}}\, - 1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,......(\ln a - \ln b = \ln \dfrac{a}{b})\]

From the question,

\[y(0) = 1\]

So,

\[

{\text{1 = }}\dfrac{c}{{2 + 0}} - 1\,\,\,\,\,\,\,\,\,\,\,......(\sin 0 = 0) \\

c = 4 \\

\]

The equation is ,

\[y = \dfrac{4}{{2 + \sin x}}\, - 1\,\,\,\]

We have asked to find \[y\left( {\dfrac{\pi }{2}} \right)\],

So,

\[y\left( {\dfrac{\pi }{2}} \right) = \,\dfrac{4}{{2 + 1}}\, - 1 = \dfrac{1}{3}\,\,\,\,\,\,\,\,\,......(\sin \left( {\dfrac{\pi }{2}} \right) = 1)\]

Hence the correct option is A.

Note: In these types of questions first open the integral by variable separation method then when the equation is obtained, get the value of constant from the information provided in the question then after getting completely , get the answer which is asked in question by putting the value of constant.

Recently Updated Pages

If ab and c are unit vectors then left ab2 right+bc2+ca2 class 12 maths JEE_Main

A rod AB of length 4 units moves horizontally when class 11 maths JEE_Main

Evaluate the value of intlimits0pi cos 3xdx A 0 B 1 class 12 maths JEE_Main

Which of the following is correct 1 nleft S cup T right class 10 maths JEE_Main

What is the area of the triangle with vertices Aleft class 11 maths JEE_Main

KCN reacts readily to give a cyanide with A Ethyl alcohol class 12 chemistry JEE_Main

Trending doubts

What was the capital of Kanishka A Mathura B Purushapura class 7 social studies CBSE

Difference Between Plant Cell and Animal Cell

Write an application to the principal requesting five class 10 english CBSE

Ray optics is valid when characteristic dimensions class 12 physics CBSE

Give 10 examples for herbs , shrubs , climbers , creepers

Tropic of Cancer passes through how many states? Name them.

Write the 6 fundamental rights of India and explain in detail

Write a letter to the principal requesting him to grant class 10 english CBSE

Name the Largest and the Smallest Cell in the Human Body ?