Question

Find S8 for the geometric series 3 + -6 + 12 + -24 +…

Answer 1

-96

-255

768

192

Answer 2

@mathslover

Answer 3

What is the common ratio here choco?

Answer 4

the ratiois 3 again

Answer 5

No. See I have ,

3 + (-6) + (12) + (-24) ...

3 * -2 = -6

-6 * (-2) = 12

12 * (-2) = -24

That is each number is getting multiplied by (-2) to get the another number of the series.

So common ratio here is (-2). Ok?

Answer 6

OK got it!

Answer 7

Do you know the formula for getting S_n of a geometric series (infinite) ?

Answer 8

^Not infinite. Its finite to 8.

Answer 9

no thats the problem that Im having

Answer 10

you there @mathslover

Answer 11

Yes, please wait.

Answer 12

ok

Answer 13

Formula : \(\cfrac{a(1-r^n)}{(1-r)} \)

Answer 14

Put r = (-2) , a = 3 and n = 8 . Solve it now.

Answer 15

ok

Answer 16

I got 257

Answer 17

Try it again. It must be negative .

Answer 18

ok -255

Answer 19

?

Answer 20

Right!

Answer 21

Good work.

Answer 22

Thank You again!

Answer 23

You're welcome and Best of Luck again ;)