Consider the given integral ∫(x2+x+1)(x6+1)(x4−x3+x−1)x5dx=∫(x2+x+1)(x6+1)(x−1)(x3+1)x5dx=∫(x6+1)(x3−1)(x3+1)x5dx=∫(x6+1)(x6−1)x5dx Let x6=t then ,6x5dx=dt This implies, ∫(x6+1)(x6−1)x5dx=61∫(t+1)(t−1)dt=121loget+1t−1+c=121logex6+1x6−1+c