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Can somebody please please please give me a step by step answer for this question?

what is the sum of a 9 term geometric series if the first term is -11 and the common ratio is -4?

Respuesta :

apologiabiology
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]