the sum of a geometric sequence is
if the first term is a and it is summed up to the nth term and r is the common ratio then
[tex]S_n= \frac{a(1-r^n)}{1-r} [/tex]
first term is -11 and the common ratio is -4 and n=9
[tex]S_9= \frac{-11(1-(-4)^9)}{1-(-4)} [/tex]
[tex]S_9= \frac{-11(1-(-262144)}{1+4} [/tex]
[tex]S_9= \frac{-11(1+262144}{5} [/tex]
[tex]S_9= \frac{-2883595}{5} [/tex]
[tex]S_9= -576719 [/tex]
