# Thread: Totally stuck and frustrated on this one! Try your hand at it!

1. ## Totally stuck and frustrated on this one! Try your hand at it!

The seq of real numbers u1, u2, u3... is such that
u(r+1) = u(r)/(1-r^2.u(r))

Using method of differences, show that
1/u1 - 1/u(N) = 1/6 (N-1)N(2N-1)

2. Originally Posted by zeromeyzl
The seq of real numbers u1, u2, u3... is such that
u(r+1) = u(r)/(1-r^2.u(r))

Using method of differences, show that
1/u1 - 1/u(N) = 1/6 (N-1)N(2N-1)
How about instead of telling us to "try our hand at it", you try your hand at it, show us what you've tried to do and where you're getting stuck?

3. To Prove It,

Sorry if i gave the impression i didn't even try, but seriously the community's really great here and i'm looking forward to help others out in future..

I tried my hand at it but only got into summation of recurrence terms- and though using method of differences pretty cuts it down alot, i just can't show the result. i do know that sum to n of r^2 is 1/6n(n+1)(2n+1).