Turn on thread page Beta
 You are Here: Home >< Maths

# Functions (factorising) question watch

1. I'm having some trouble with this question to do with factorising a cubic equation... I have no idea what to do with the given information.

2. The factor theorem is; if f(a)=0, then (x-a) is a factor of f(x), this would mean (x-a)(some quadratic factor) = 0. You can use algebraic long division to solve for the quadratic factor.
3. (Original post by Gabzinc)
I'm having some trouble with this question to do with factorising a cubic equation... I have no idea what to do with the given information.

If f(-4) =0 you know that x+4 is a factor of it. Start by factorising that out

Posted from TSR Mobile
4. (Original post by NotNotBatman)
The factor theorem is; if f(a)=0, then (x-a) is a factor of f(x), this would mean (x-a)(some quadratic factor) = 0. You can use algebraic long division to solve for the quadratic factor.
(Original post by BobBobson)
If f(-4) =0 you know that x+4 is a factor of it. Start by factorising that out
I've never studied factor theorem or factorising cubics before. I'll give it some practice tonight.

Thanks guys.
5. (Original post by Gabzinc)
I'm having some trouble with this question to do with factorising a cubic equation... I have no idea what to do with the given information.

Since you've been given that x=-4 is a root that must mean you can write the polynomial in the form:

(x + 4) times a quadratic. Simple log division will give you the quadratic:

f(x) = (x+4)(2x^2 -x -3)

Now you just have to factor the quadratic. Try a few things. You should quickly discover that the full factorization is:

f(x) = (x+4)(x+1)(2x-3)

So the roots of f(x) = 0 are -4, -1, 3

Hopefully this helps.
6. (Original post by sameehaiqbal)
Hopefully this helps.
Unfortunately providing a full solution rarely helps and that is why it is frowned upon here. Please read the Forum Rules pinned to the top of the Maths Forum.
7. (Original post by Mr M)
Unfortunately providing a full solution rarely helps and that is why it is frowned upon here. Please read the Forum Rules pinned to the top of the Maths Forum.
Lol, sorry. I wasn't aware. I was just trying to help.
8. (Original post by sameehaiqbal)
Lol, sorry. I wasn't aware. I was just trying to help.
I know you meant well.

Turn on thread page Beta

### Related university courses

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:
Updated: January 8, 2017
Today on TSR

### Exam Jam 2018

Join thousands of students this half term

Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups

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