Question

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What is the sum of the first 7 terms of the series −8 +16 −32 + 64−... ?

Answer 1

Hello there,

What is the sum of the first 7 terms of the series −8 +16 −32 + 64−... ?

Answer: -258

Answer 2

Answer: -258

Explanation:

Given the sequence {-8, 16, -32, 64, ... , a₇} we know the following

• the first term (a₁) = -8
• the common ratio (r) = -2
• the number of terms (n) = 7

Input the information above into the Sum formula:

`S_n=(a_1(1-r^n))/(1-r)\\\\S_7=(-8(1-(-2)^7))/(1-(-2))\\\\.\quad =(-8(1-(-128)))/(1+3)\\\\.\quad =(-8(129))/(4)\\\\.\quad =-2(129)\\\\.\quad =-258`