Instead of doing your problem for you, I will do one EXACTLY IN EVERY
DETAIL like yours, so that when you do yours, you can use this as a
model.

I will find the sum of this infinite geometric series instead:



We should first check to see if it really is a geometric series, for sometimes
books contain errors/typos.  If it is a geometric series then this must be true:



So we calculate the three ratio to see if they are all equal:







They are all the same so it is a geometric series with common ratio = 

It is a geometric series with a defined sum when taken to infinitely many
terms because the ratio  is greater than -1 and less than +1.

, where a1 = 1st term = 



Answer to this problem = 

Now do your problem EXACTLY the same way.

Edwin