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What is the sum of the first 7 terms of the series − 3 + 6 − 12 + 24 −... ?

PLEASE HELP ASAP!!! CORRECT ANSWER ONLY PLEASE!!! What is the sum of the first 7 terms-example-1

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Answer: -129

Explanation:

Given the sequence {-3, 6, -12, 24, ... }, we can see that the first term (a) is -3 and the ratio (r) is
(6)/(-3) = -2.

Input those values into the Sum formula:


S_n=(a(1-r^n))/(1-r)\\\\S_7=(-3(1-(-2)^7))/(1-(-2))\\\\.\quad=(-3(1-(-128)))/(1+2)\\\\.\quad=(-3(1+128))/(3)\\\\.\quad=(-3(129))/(3)\\\\.\quad=-129

User Sourabh Agrawal
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