Practicing Success
$∫\frac{3+2\cos x}{(2+3\cos x)^2}dx$ is equal to |
$(\frac{\sin x}{3\cos x+2})+c$ $(\frac{2\cos x}{3\sin x+2})+c$ $(\frac{2\cos x}{3\cos x+2})+c$ $(\frac{2\sin x}{3\sin x+2})+c$ |
$(\frac{\sin x}{3\cos x+2})+c$ |
Let $I=∫\frac{3+2\cos x}{(2+3\cos x)^2}dx$ Multiplying numerator and denominator by cosec2x, we get $I=∫\frac{3cosec^2x+2\cot x\,cosecx}{(2cosecx+3\cot x)^2}dx=-∫\frac{-3cosec^2x-2cotx\,cosecx}{(2cosecx+3\cot x)^2}$ $=\frac{1}{2cosecx+3cotx}+c=(\frac{sinx}{2+3cosx})+c$ Hence (A) is the correct answer. Alternative: $I=∫\frac{3sin^2x+3cos^2x+2cosx}{(2+3cosx)^2}dx$ $=∫\frac{cosx}{(2+3cosx)}dx+∫\frac{3sinx.sinx}{(2+3cosx)^2}dx$ $=∫\frac{cosx}{2+3cosx}dx+\frac{sinx}{2+3cosx}-\int\frac{cosx}{2+3cosx}dx=\frac{sinx}{2+3cosx}+c$ |