Answer: -258
Step-by-step 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:
[tex]S_n=\dfrac{a_1(1-r^n)}{1-r}\\\\S_7=\dfrac{-8(1-(-2)^7)}{1-(-2)}\\\\.\quad =\dfrac{-8(1-(-128))}{1+3}\\\\.\quad =\dfrac{-8(129)}{4}\\\\.\quad =-2(129)\\\\.\quad =-258[/tex]
