Hi everyone, 1. The problem statement, all variables and given/known data My problem is just to derive a simple formula, which is http://www.texify.com/img/%5Cnormalsize%5C%21%28-1%29%5E%7Br%28r%2B1%29/2%7D%20%3D%5Csqrt%7B2%7D%20%5Cmbox%7Bcos%7D%20%5Cfrac%7B%5Cpi%7D%7B4%7D%282r%2B1%29.gif [Broken] Here r is a positive integer. 3. The attempt at a solution I verified this formula by inserting r=4k ~ 4k+3 (k=0,1,2....), but I still have no idea how to derive it from the left hand side of the equation. Could anyone please help me out? Any help is appreciated.