Saturday, 26 July 2014

integration - How can I prove that inttextsech(x) mathrmdx=sin1(tanh(x))+c?



How can I prove that
sech(x) dx=sin1(tanh(x))+c?


I don’t know how to prove this identity. Any help?




I tried to multiply by cosh(x)cosh(x), and everything is okay, but at last I didn’t get the same answer.


Answer



Since you know the result, why not just differentiate it:
(arcsin(tanhx))=(tanhx)×11(tanhx)2=(sechx)2×1(sechx)2=sechx.





I don’t know how to prove this identity. Any help?




This proves that
sechxdx=arcsin(tanhx)

up to a constant.







Edit: you might want to write
sechxdx=(sechx)2×1(sechx)2dx=(tanhx)×11(tanhx)2dx=arcsin(tanhx)+C.



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