# Permutation proof

• Oct 26th 2010, 05:44 PM
guyonfire89
Permutation proof
I have a problem where the question is, Prove

$\frac{1}{2}P(2,1)+\frac{2}{3}P(3,2)+\frac{3}{4}(4, 3)+...+\frac{n}{n+1}P(n+1,n)=(n+1)!-1$

How do I start this? Do I use mathematical induction?
• Oct 27th 2010, 07:02 AM
emakarov
Is $\displaystyle P(n,k)=\frac{n!}{(n-k)!}$? Then yes, the statement can be easily proved by induction.