f(x)=∫0xcost/(1+sin2t)dt,求∫0π/2f’(x)/(1+f2(x))dx.

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问题 f(x)=∫0xcost/(1+sin2t)dt,求∫0π/2f’(x)/(1+f2(x))dx.

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答案0π/2f’(x)/(1+f2(x))dx=∫0π/21/(1+f2(x))df(x)=arctanf(x)|0π/2=arctanf(π/2),因为f(π/2)=∫0π/2cost/(1+sin2t)dt=arctan(sint)|0π/2=π/4,所以原式等于arctanπ/4.

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