You are Here: Home >< Maths

# C2 geometric series question

Announcements Posted on
Why bother with a post grad course - waste of time? 17-10-2016
1. The first three terms of a geometric series are 4p, (3p + 15) and (5p + 20) respectively,where p is a positive constant.

Show that 11p2 – 10p – 225 = 0

Eh?
2. (Original post by jessyjellytot14)
The first three terms of a geometric series are 4p, (3p + 15) and (5p + 20) respectively,where p is a positive constant.

Show that 11p2 – 10p – 225 = 0

Eh?
Well, what does your gut instinct tell you to do?

Hint:
Spoiler:
Show
it has something to do with 'r', the common ratio.
3. for any GP there is a way of finding the common ratio r using consecutive terms...
4. (Original post by jessyjellytot14)
The first three terms of a geometric series are 4p, (3p + 15) and (5p + 20) respectively,where p is a positive constant.

Show that 11p2 – 10p – 225 = 0

Eh?
What do you know about consecutive terms in a geometric series? They have a common ratio.

The ratio of the second term to the first is the same as the ratio of the third term to the second, etc...

So . Here we have: , now multiply out and simplify into the given quadratic.
5. (Original post by SeanFM)
Well, what does your gut instinct tell you to do?

Hint:
Spoiler:
Show
it has something to do with 'r', the common ratio.
I'll try doing ar/a = ar2/ar
6. (Original post by jessyjellytot14)
I'll try doing ar/a = ar2/ar
Update: It worked
7. (Original post by jessyjellytot14)
Update: It worked
Well done!

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 22, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### A level maths

Which modules should I take?

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams