∫-π/4π/4sin4x/(1+ex)dx=________·

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问题-π/4π/4sin4x/(1+ex)dx=________·

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答案3π/32-1/4

解析 因为对[-a,a]上连续的函数f(x)有∫-aaf(x)dx=∫0a[f(x)+f(-x)]dx,所以∫-π/4π/4sin4x/(1+ex)dx=∫0π/4sin4x[1/(1+ex)+1/(1+e-x)]dx=∫0π/4sin4xdx=∫0π/4[(1-cos2x)/2]2dx=1/8∫0π/2(1-cost)2dt=1/8∫0π/2(1-2cost+cos2x)dt=π/16-1/4∫0π/2costdt+1/8∫0π/2cos2tdt=π/16-1/4+1/8×1/2×π/2=3π/32-1/4.
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