求一下11和15题

(11)
u^2
=u(1+u) -u
=u(1+u) -(1+u) +1
let
u= (x+2)^(1/3)
du = (1/3)(x+2)^(-2/3) dx
dx= 3u^2 du
∫ dx/[1 +(x+2)^(1/3)]
=∫ 3u^2 du/(1+u)
=3∫ [ u-1 +1/(1+u) ] du
=(3/2)u^2 -3u + 3ln|1+u| + C
=(3/2)(x+2)^(2/3) -3(x+2)^(1/3) + 3ln|1+(x+2)^(1/3)| + C

(15)
∫ x^2.sinx dx
=-∫ x^2 dcosx
=-x^2.cosx +2∫ xcosx dx
=-x^2.cosx +2∫ x dsinx
=-x^2.cosx +2xsinx -2∫ sinx dx
=-x^2.cosx +2xsinx +2cosx + C