Question

Evaluate

Answer 1

\[\sum_{n=1}^{7}2(-2)^{n-1}\]

Answer 2

do you need to determine A7 or Sn?

Answer 3

sn

Answer 4

is the first number 2?

Answer 5

If n=1, then the first number would indeed be 2(-2)^(1-1)=2. Yes!

Answer 6

whats the last number?

Answer 7

Try evaluating that yourself: instead of using n=1, use n=7.

Answer 8

what is "d"? (difference)
use it to find n=7

Answer 9

dinner time, good luck

Answer 10

@ehuman : forgive me for this caution, but I don't believe this is an arithmetic sequence. On the contrary, I think it's a geometric sequence.

Answer 11

is the answer 84?

Answer 12

I got 86. I don't know which of us is correct, but it's promising that we have answers that close.

Answer 13

86 is correct

Answer 14

I'm glad. But could I help you determine why y ou got 84?

Answer 15

Is it worth your time? or have you other questions?