AP EAMCET · Maths · Differential Equations

If $- \frac{π}{4} < x < \frac{π}{4},$ then the general solution of the differential equation $\cos^{2} x \cdot \frac{d y}{d x} - (\tan 2 x) y = \cos^{4} x$ is

A $y = \frac{1}{2} [\frac{\tan 2 x + c}{1 - \tan^{2} x}]$
B $y = \frac{1}{2} [\frac{\cos 2 x + c}{1 - \tan^{2} x}]$
C $y = \frac{1}{2} [\frac{\sin 2 x + c}{1 - \tan^{2} x}]$
D $y = \frac{1}{2} [\frac{\sin x + c}{1 - \tan^{2} x}]$

Verified Solution

Answer & Solution

Correct Answer

(C) $y = \frac{1}{2} [\frac{\sin 2 x + c}{1 - \tan^{2} x}]$

Step-by-step Solution

Detailed explanation

Given, cos2x·dydx-(tan2x)y=cos4x ⇒dydx-tan2xcos2xy=cos4xcos2x ⇒dydx-tan2xcos2xy=cos2x This is the linear differential equation of the form dydx+Py=Q. Therefore, we get P=-tan2xcos2x and Q=cos2x I.F. =e∫Pdx Now, ∫Pdx=-∫tan2xcos2xdx…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Explore more questions on app

From AP EAMCET

Explore more questions on app

If -π4<x<π4, then the general solution of the differential equation cos2x·dydx-(tan2x)y=cos4x is

Step-by-step Solution

If $- \frac{π}{4} < x < \frac{π}{4},$ then the general solution of the differential equation $\cos^{2} x \cdot \frac{d y}{d x} - (\tan 2 x) y = \cos^{4} x$ is