Question

Find the sum of the geometric series –5, -10, -20, -40, . . . for 7 terms.

Answer 1

I suppose the answer is -635
can any1 reassure me

Answer 2

The formula needed is:
\[S _{n}=\frac{a(r ^{n}-1)}{r-1}\]
Where a is the first term and r is the common ratio.
So plugging the values into the formula:
\[S _{n}=\frac{-5(2^{7}-1)}{2-1}=you\ can\ calculate\]

Answer 3

is it - 635??

Answer 4

I calculated it

Answer 5

@kropot72

Answer 6

Correct!

Answer 7

thanks

Answer 8

You're welcome :)