Question

1. What is the sum of the geometric sequence 8, –16, 32 … if there are 15 terms? (1 point)
2. What is the sum of the geometric sequence 4, 12, 36 … if there are 9 terms? (1 point)
3. What is the sum of a 6-term geometric sequence if the first term is 11, the last term is –11,264 and the common ratio is –4? (1 point)
4. What is the sum of an 8-term geometric sequence if the first term is 10 and the last term is
781,250? (1 point)

Answer 1

needd help on these 4.

Answer 2

@ganeshie8

Answer 3

use the geometric series formula

Answer 4

1. What is the sum of the geometric sequence 8, –16, 32 … if there are 15 terms? (1 point)

Answer 5

sn=a1-a1^rn/1-r . right ?

Answer 6

That looks arithmetic to me.

Answer 7

HAHA YEAH . Mybad.

Answer 8

I had a brain fart for a minute.

Answer 9

All of these questions ask for the sum of a geometric sequence. The formula for that sum is:
\[S _{n}=\frac{a _{1}(1-r^n)}{1-r}\]

Answer 10

For the first one, the first term is 8 so a_1=8
You always multiply by -2 to get the next term so r=-2
There are 15 terms so n = 15. Plug into the formula and simplify.

Answer 11

what ? i thought geometric sequence was an=a1-a1^rn/1-r

Answer 12

Ok. Do what you want. I have shown you the formula and how to do the problem but you are perfectly free to do whatever you want.

Answer 13

cool

Answer 14

forget it .

Answer 15

yo give it a try