∫ xcos(x/3) dx ...

问题描述:

∫ xcos(x/3) dx ...

∫ xcos(x/3) dx
=3∫ xdsin(x/3)
=3xsin(x/3)-3∫ sin(x/3)dx+C
=3xsin(x/3)+9cos(x/3)+C
C为任意常数