>>11561598cancel the 5! with the 4! to get 5x5 in the parenthesis. take the sqrt you got 5. so you got a sum of 5s with alternating sign, starting off negative inside the sum. first negative cancels with the next which is positive, second negative cancels with next (fourth) which is positive... the 461th 5er has negative sign so is followed by the negative 461th-2 and the cancelling positive 461th-1er so the sum results in -5. we apply the sum negation and get 5.
