I have been practicing power series problems and a lot of them include factorials. To find out if they converge or not I'll often use the ratio test. However, I never quite understood how to cancel factorials when replacing the n with n+1. i.e. the textbook has an example problem that shows that [(n+1)!]2 ⇒ (n+1)2 (n!) How is this done? Thank you in advance.