Permutation problem

  • #1

Homework Statement



Prove that 1/2 P(2,1) + 2/3 P(3,2)+3/4 P(4,3)+ ... + n/(n+1) P(n+1,n) = (n+1)! - 1

Please help!

Homework Equations


P(n,r) = n!/(n-r)!


The Attempt at a Solution


The inequation can be simplified to:
1*1! + 2*2! + 3*3!+ ... + n*n! = (n+1)! - 1 (*)
Use the induction method:
1/Base case: n=1 -> 1=1 true
2/Inductive case: suppose (*) is true
Need to prove: 1*1! + 2*2! + 3*3!+ ... + (n+1)*(n+1)! = (n+2)! -1
 

Answers and Replies

  • #2
lanedance
Homework Helper
3,304
2
i think you;re pretty much there, so assume f(n) = (*) is true, then you need to show
f(n+1) = (n+2)! - 1 = f(n) + (n+1)(n+1)!

substituting for f(n) gives
(n+2)! - 1 = (n+1)! - 1 + (n+1)(n+1)!
 

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