Was wondering if anyone could help me out. I have the answers but one step i just can't get my head around.
In a geometric progression, the second term is -4 and the sum to infinity is 9. Find the common ratio.
ar = -4
a/1-r = 9
And then in the answers they jump from that to: -4/r = 9-9r
I just can't see why, and i'm probably being silly! Anyone help me out?
From the first equation: a = -4/r
From the second equation: a = 9(1-r) = 9-9r
So we have a= -4/r = 9-9r.
set both equations equal to 'a' then set them equal to each other then solve!!!
Thank you so much guys!
I see it now. *facepalm* I was being very thick.
Appreciate the help.
So what's the answer please? I ended up with two answers which can't be right (i guess I'm being thick seeing as this is last year's stuff)
you know the sum to infinity is 9 so if you sub in both of your answers only one will equal 9.. this is the correct answer
Thanks for posting! You just need to create an account in order to submit the post
Already a member?
Oops, something wasn't right
please check the following:
Not got an account?
Sign up now
© Copyright The Student Room 2016 all rights reserved
The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.
Register Number: 04666380 (England and Wales), VAT No. 806 8067 22
Registered Office: International House, Queens Road, Brighton, BN1 3XE