improper integration

2011-12-04 10:26 pm
Evaluate ∫_[0~∞] exp(-4x- √5/x)cos(3x) /√x dx

求值 ∫_[0~∞] exp(-4x- √5/x)cos(3x) /√x dx

回答 (3)

2011-12-06 10:09 pm
It is easy to change to integration on the positive real line by suitable sector contour integral.
2011-12-06 11:49 am
CRebecca,你又衰心急了!難度你不覺得自由自在的做法有問題嗎?

留意A的代入法,須留意√a是複數,那麼會導致lower limit和upper limit真的仍然是分別為0和∞嗎?

雖然在數值上看似做對了(http://www.wolframalpha.com/input/?i=integrate+e%5E%28-4x-5%5E%281%2F2%29%2Fx%29cos%283x%29%2Fx%5E%281%2F2%29%2Cx%2C0%2Cinf),但是這樣的做法真的認可嗎?


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