anpanman SG If f(r) = r(r+1)!, simplify f(r) - f (r -1) and hence find in terms of n, the series 5.2! + 10.3! +...+ (n^2 + 1) n! I got n(n+1)! but answer is n(n+1)! - 2
wee_ws SG Hi, A good way to check is by substitution. Let n = 1, is 5.2! = 2.3! or 2.3! - 2? Let n = 2, is 5.2! + 10.3! = 3.4! or 3.4! - 2? Do check your cancellation of terms again. Thanks!Cheers, Wen Shih