计算∫xcosx/3dx;数学基础差,注:课本上的答案为3xsinx/3+9cosx/3+c;谢谢

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计算∫xcosx/3dx;数学基础差,注:课本上的答案为3xsinx/3+9cosx/3+c;谢谢

分部积分法:
∫xcos(x/3)dx
=3∫xdsin(x/3)
=3[xsin(x/3)-∫sin(x/3)dx]
=3[xsin(x/3)-3∫sin(x/3)d(x/3)]
=3xsin(x/3)+9cos(x/3)+C

分部积分法:3 ∫xdsinx/3=3(xsinx/3-sinx/3dx)=3(xsinx/3+3cosx/3)+c=3xsinx/3+9cosx/3+c 希望对你有帮助~