If a partial sum of a series is given this way: http://latex.codecogs.com/gif.downlo...space;}{3^{n}}

Then, can I say since the http://latex.codecogs.com/gif.downlo...e;}{3^{n}}=243,

http://quicklatex.com/cache3/ql_022a...9c4f211_l3.png

Is this right? Can I do this to find the series of the partial sum equation of http://quicklatex.com/cache3/ql_c6ae...23aae0d_l3.png?

Thanks!