Question

An infinite geometric series has a first term a1=15 and a sum of 45. Explain how you can use the formula S=a1/(1-r) to find the value of the common ratio. What is the value of r? Attach a screenshot of your work

Answer 1

@dude
i dont know

Answer 2

lol kk Thx!

Answer 3

can you help her

Answer 4

dude

Answer 5

@Ultrilliam
can you help her

Answer 6

Oh this is straightforward

They already give you the formula to find the rate

\(\sum=\dfrac{a_1}{(1-r)}\)

\(\sum \) is just sum


You know the sum and the \(a_1\) value, just substitute them both in and isolate r


Do you know how to do that or are you confused?

Answer 7

confused cause as soon as I put those into the equation I can't figure out how to get r by itself.

Answer 8

What equation do you have right now?

Answer 9

S=a1/(1-r)
45=15/(1-r)

Answer 10

Yeah looks good

\(45=\dfrac{15}{(1-r)}\)

Because of the awkward nature of the denominator, we just want to multiply the whole factor by the denominator

\(\color{green}{(1-r)~\times } ~45=\dfrac{15}{\color{red}{\cancel{(1-r)}}}\color{red}{\cancel{{\times (1-r)}}}\)

Answer 11

Oh! okay! Thank you!