Question

find a1 for the geometric series r=-1 and s11=7

Answer 1

Use the formula
\[S _{n}=\frac{a _{1}(r ^{n}-1)}{r-1}\]
\[7=\frac{a _{1}(-1^{11}-1)}{-1-1}\]
\[a _{1}=\frac{7\times-2}{(-1^{11}-1)}=you\ can\ calculate\]

Answer 2

i got 7

Answer 3

Good work! Your answer is correct :)

Answer 4

( : thanks

Answer 5

You're welcome :)