Question 986528
<pre>
a<sub>1</sub> = first term = 9
r = {{{-1/3}}} = common ratio

First substitute those in this equation: 

{{{S[infinity]}}}{{{""=""}}}{{{a[1]/(1-r)}}}

Then simplify by multiplying top and bottom by LCD= 3

If you have trouble completing it, ask me in the 
thank-you note form below.

Edwin</pre>