Concept:Simplify the integrand using trigonometric identities, then substitute t=sinx to integrate easily.Explanation:Write cos3x=cosx⋅cos2x=cosx(1−sin2x).So, I=∫sin2x+sinxcosx(1−sin2x)dx.Factorize: sin2x+sinx=sinx(1+sinx) and 1−sin2x=(1−sinx)(1+sinx).Cancel (1+sinx) from numerator and denominator.Thus, I=∫sinxcosx(1−sinx)dx.Let t=sinx, then dt=cosxdx.So I=∫t1−tdt=∫(t1−1)dt.Integrate: I=log∣t∣−t+c.Substitute back t=sinx: I=log∣sinx∣−sinx+c.Answer:log(sinx)−sinx+c, where c is a constant of integration.Correct option: A.