Question 924963
Find the sum of first 7 terms 4,12,36?
<pre>
This is a geometric progression (GP) so use the formula for the sum of a G.P.: 
{{{S[n] = a[1]*((1 - r^n)/(1 - r))}}}
{{{n = 7}}}
{{{S[n]}}} is the sum of the series you're seeking
{{{a[1] = 4}}}
Common ratio or {{{r = 3}}}