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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?

User Shneur
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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

S_n= (a(1-r^n))/(1-r)
first term is -11 and the common ratio is -4 and n=9


S_9= (-11(1-(-4)^9))/(1-(-4))

S_9= (-11(1-(-262144))/(1+4)

S_9= (-11(1+262144)/(5)

S_9= (-2883595)/(5)

S_9= -576719
User Zet
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