红线处是直接套公式得来的
有任何疑惑,欢迎追问
令 x+1/2 = (1/2)secu, 则 d(x+1/2) = (1/2)secutanudu
I = ... = ∫(1/2)secutanudu/[(1/2)tanu] = ∫secudu
= ln|secu+tanu| + C1 = ln|(1/2)secu+(1/2)tanu| + C
= ln|(1/2)secu+√(secu/2)^2-(1/2)^2| + C
= ln|(x+1/2)+√[(x+1/2)^2-(1/2)^2]| + C = ......