Sum to infinity question: sum is 9/2, a_2 = -2; find r, a_n

[Peter Burnes]

This is exciting stuff... a little tricky but very cool

the sum to infinity of a geometric series is 9/2
The SECOND term in the series is -2
Find the value of r, the common ratio of the series.

Anyone have any ideas? I can't seem to find a good answer for r. It would be grand if we can find a...
:roll:

 

[royhaas]

Solve \(\displaystyle \L \,\frac{a}{1\,-\,r}\,=\,\frac{9}{2},\,\, ar\,=\,-2.\)

 

[Peter Burnes]

Thanks for the advice...it worked out well!
Isn't maths fun!!