Prove :
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Try this.. tan(x)=sin(x)/cos(x) and cot(x) = cos(x)/sin(x) add them both you get c^2+s^2/c*s = 1/c*s then it would become integral between 0 and pi/2 --> ln (1/cos(x)*sin*(x)) dx ... now you know sin(2x)=2sin(x)cos(x) see what you get form here...
I think of another method , old method is to transform it to this famous integral : . Let Then Sub. we have Therefore , Sub. Finally note that so
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