∫(x^2)cos(x/2)dx用分部积分法

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∫(x^2)cos(x/2)dx用分部积分法
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∫(x^2)cos(x/2)dx用分部积分法
∫(x^2)cos(x/2)dx用分部积分法

∫(x^2)cos(x/2)dx用分部积分法
如果答案是(1/6)x^3+(1/2)(x^2)sinx+xcosx-sinx+C,那么你的题目抄错咯,题目应该是:
∫x²cos²(x/2) dx,那么
∫ x²cos²(x/2)dx
=∫1/2x²(1+cosx)dx
=1/2∫ x²dx+∫1/2x²cosxdx
=1/6 x³+1/2∫x²dsinx
=1/6 x³+1/2 x²sinx-∫xsinxdx
=1/6 x³+1/2 x²sinx-[-xcosx+∫cosxdx]
=1/6 x³+1/2 x²sinx+ xcosx-sinx+C
如果题目是∫ x²cos(x/2)dx,那么,参考答案错了,正确的答案是:
∫ x²cos(x/2)dx=∫2x²dsin(x/2)
= 2x²sin(x/2)- ∫2 sin(x/2) dx²
=2x²sin(x/2)- ∫4xsin(x/2) dx
=2x²sin(x/2)- ∫-8x dcos(x/2)
=2x²sin(x/2)+8xcos(x/2)- ∫8cos(x/2)dx
=2x²sin(x/2)+8xcos(x/2)- 16sin(x/2)+C