Question

What is the sum of the first seven terms of the geometric series where a1 = 10 and r =-2?
Answers:
s7 = 640
s7 = -430
s7 = 430
s7 = -213

Answer 1

What do we know about this question

Answer 2

We have to understand it to answer it

Answer 3

Can you identify the first term?
The common ratio is r=-2. This means that each succeeding term is found from the previous term by multiplying the previous term by -2.

There is a formula for the sum of an infinite geometric series. It looks like this:\[\frac{ a }{1-r }\] but that's ONLY for a series that goes on and on.

What if you're interested only in the first 7 terms? There's a formula for that also. Can you find it? (Look up "sum of n first terms of a geometric series."

Answer 4

We know the ratio and the first part of the equation a1 which is 10

Answer 5

the ratio is -2

Answer 6

@ Snufflebug02:

Look up the following:

http://www.purplemath.com/modules/series5.htm

Answer 7

@Snufflebug02 Please use the Internet link provided above.