求下列不定積分 ∫(arctan e^x)/(e^2x)dx
(-1/2)[e^-(2x)*arctane^x+arctane^x+e^(-x)]+C
我的解法是：原式= ∫(arctan e^x)/(e^x)d(1/e^x)
令1/e^x=t = ∫(arctan 1/t)/t dt
= (-1/2) ∫(arctan 1/t) d(t^2)
= (-1/2) [(t^2)(arctan 1/t) - ∫(t^2)d(arctan 1/t)]
= (-1/2) [(t^2)(arctan 1/t) + ∫(t^2)/(1+t^2)dt]
= (-1/2) [(t^2)(arctan 1/t) + ∫(t^2+1-1)/(1+t^2)dt
= (-1/2) {(t^2)(arctan 1/t) +∫1-[1/(1+t^2)]dt}
= (-1/2)[e^-(2x)*arctane^x-arctane^(-x)+e^(-x)]+C
不知道自己哪步算錯(cuò)了,和答案總是差一個(gè)數(shù)啊,是第一步換元有問題嗎?