Practicing Success
If $\int\frac{\sin^8x-\cos^8x}{1-2\sin^2x\cos^2x}dx=A\sin 2x+B$, is: |
$A=-\frac{1}{2}$ $A=\frac{1}{2}$ A = – 1 A = 1 |
$A=-\frac{1}{2}$ |
$\int\frac{\sin^8x-\cos^8x}{1-2\sin^2x\cos^2x}dx=\int\frac{(\sin^4x-\cos^4x)(\sin^4x+\cos^4x)}{(1-2\sin^2x\cos^2x)}dx$ $=\int\frac{(\sin^2x-\cos^2x)(\sin^2x+\cos^2x)}{(1-2\sin^2x\cos^2x)}×[(\sin^2x+\cos^2x)^2-2\sin^2x\cos^2x]dx$ $=\int\frac{\cos 2x.(1-2\sin^2x\cos^2x)}{(1-2\sin^2x\cos^2x)}dx=-\int\cos 2x\,dx=\frac{-1}{2}\sin 2x+B⇒A=\frac{-1}{2}$ |