P185 判断广义积分的敛散性,若收敛计算其值 1 .∫[0,+∞](e^-x)sinxdx

2024-12-23 04:23:01
推荐回答(1个)
回答1:

你好!

∫[0,+∞](e^-x)sinxdx
= ∫[0,+∞] - sinx de^(-x)
= -sinx e^(-x) |<0,+∞> + ∫[0,+∞] e^(-x) dsinx
= ∫[0,+∞] e^(-x) cosx dx
= ∫[0,+∞] - cosx de^(-x)
= -cosx e^(-x) |<0,+∞> + ∫[0,+∞] e^(-x) dcosx
= 1 - ∫[0,+∞] e^(-x) sinx dx
∴ ∫[0,+∞] e^(-x) sinx dx = 1/2