Question

Find S7 for the geometric series 2 + -6 + 18 + -54 +…

Answer 1

what 57

Answer 2

i think it is S 7

Answer 3

a=2
\[r=\frac{ -6 }{ 2 }=-3\]
\[Sn=\frac{ a \left( 1-r ^{n} \right) }{ 1-r }\]
Plug n=7 and find S7