∫(cosx)^5dx =∫纯卖(cosx)^4 cosdx
= ∫ (1-sin^2 x)^2 d(sinx)
=∫[1-2(sinx)^2+(sinx)^4]d(sinx)
=sinx-2/3*(sinx)^3+1/5*(sinx)^5+C
∫sin3xsin5xdx
=1/2*∫[ cos2x-cos8x]dx
=1/2*∫ cos2xdx-1/2*∫cos8xdx
=1/4∫瞎升 cos2xd(2x)-1/16∫做神逗 cos8xd(8x)
=1/4*sin2x-1/16*sin8x+C