Given and
Deduce
Use this result to show
I was thinking geometric series but cant seem to figure it out. It can easily be done using sums to products but i was wondering if there was a way which makes use of the given result.
thanks
This is a geometric series with common ratio and sum . Divide top and bottom of that by and you will have something that you can express in terms of sines.
For the second part (which should have an extra term +2n as shown), take the formula for the first part, replace by and use the formula .