Hi everyone, I have a couple questions that have been gnawing at my head for some time: Why is it that on wikipedia for the example logarithms and residue at infinity, (on the methods of conour integration link) that the integral is not zero? there are no isolated singularities inside the contour, there fore by the residue theorem it should be zero. Also, when i go around the countour of sqrt(z^2-1) i.e. the one encircling the two branch points in the counter clockwise sense, I always get that lim y to zero- is -isqrt(x^2-1) and y to zero+ is the negative of that. The answer though, is isqrt(1-x^2) and the negative of that for lim 0-. Why am i wrong? Help would be greatly appreciated Thanks!