Question

请教一道反常积分的题

请教一道反常积分的题请问划线部分是怎么来的

Answer 1

1/[e^(x+1) + e^(3-x)] = e^(x-3)/[e^(2x-2)+1] = (1/e^2)e^(x-1)/[e^(2x-2)+1]
原式 = (1/e^2)∫d[(e^(x-1)]/[e^(2x-2)+1] = ......