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## anonymous one year ago Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 8 terms and select the correct answer below.

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1. anonymous

–195,312 195,312<-----my answer 292,968 –292,968

2. campbell_st

good choice.

3. anonymous

a=3 $r=\frac{ 15 }{ 3 }=-5$ $S _{n}=\frac{ a \left( r^n-1 \right) }{ r-1 }$ $S _{8}=\frac{ -3\left\{ \left( -5 \right)^8-1 \right\} }{ -5-1 }$ ?

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