Choose the correct answer.
∫cos 2x(sin x+cos x)2dx is equal to(a)−1sin x+cos x+C(b)log|sin x+cos x|+C(c)log|sin x−cos x|+C(d)1(sin x+cos x)2+C
Let I=∫cos 2x(sin x+cos x)2dx=∫cos2x−sin2x(sin x+cos x)2dx [∵ cos 2x=cos2x−sin2x]=∫(cos x−sin x)(cos x+sin x)(sin x+cos x)(sin x+cos x)dx=∫cos x−sin xsin x+cos xdxPut sin x+cos x=t⇒(cos x−sin x dx=dt)∴ I=∫cos x−sin xtdtcos x−sin x=∫1tdt=log|t|+C=log|sin x+cos x|+C.
Hence, the option (b) is correct.