Practicing Success
$\int \frac{\sin x}{\sin x-\cos x} d x$ is equal to : |
$\frac{x}{2}-\frac{1}{2} \log (\sin x-\cos x)+c$ $\frac{x}{2}+\frac{1}{2} \log (\sin x-\cos x)+c$ $\frac{x}{2}+\frac{1}{2} \log (\sin x+\cos x)+c$ none of these |
$\frac{x}{2}+\frac{1}{2} \log (\sin x-\cos x)+c$ |
Let sin x = A( sin x – cos x) + B. d.c of (sin x – cos x) or sin x = A ( sin x – cos x) + B ( cos x + sin x) or sin x= (A + B ) sin x + (B –A) cos x equating the coefficient of sin x and cos x, we get A + B = 1 and B – A = 0 A = 1/2, B = 1/2 $I =\int \frac{\frac{1}{2}(\sin x-\cos x)+\frac{1}{2}(\cos x+\sin x)}{\sin x-\cos x}$ $=\frac{1}{2} \int d x+\frac{1}{2} \int \frac{\cos x+\sin x}{\sin x-\cos x} d x=\frac{x}{2}+\frac{1}{2} \log (\sin x-\cos x)+c$ Hence (2) is the correct answer. |