You are Here: Home >< Maths

# [Core 4] Rational Fractions

Announcements Posted on
Why bother with a post grad course - waste of time? 17-10-2016
1. Here is the question:

I did
A(x+1)(x+5) + B(x-1)(x+5) + C(x-1)(x+1) = 3x2 + 28x + 17

Then to work out each constant:

A: let x = 1
12A = 3 + 28 + 17 => A = 4

B: let x = -1
-8B = 3 - 28 + 17 => B = 4

C: let x = -5
24C = 192 - 140 + 17 => C = 2.875

However when I add my three fractional components on WolframAlpha, I do not get the same answer as I what I am trying to express.

Help would be appreciated, thanks.
2. Mistake on B and C,

-8B = 3-28+17

-8B = -8

so B=....

and For C, 3(-5)^2 = 75 not 192
3. (Original post by NotNotBatman)
Mistake on B and C,

-8B = 3-28+17

-8B = -8

so B=....

and For C, 3(-5)^2 = 75 not 192
Damn.. My mistakes were so stupid. I got B = 1 and C = - 2, is this correct?
4. (Original post by DarkEnergy)
Damn.. My mistakes were so stupid. I got B = 1 and C = - 2, is this correct?
Yes, that's correct.
5. (Original post by NotNotBatman)
Yes, that's correct.

## 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: October 4, 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