You are Here: Home

# Factorising

Announcements Posted on
Uni student? You could win a Samsung Galaxy S7 or £500 of travel vouchers by taking this quick survey 05-05-2016
Talking about ISA/EMPA specifics is against our guidelines - read more here 28-04-2016
1. (Original post by zed963)
So the above is right,

So if i had this expression : 6y(x+3y)+9(x+3y)^2

Would that be (x+3y) and something which I can't figure out HELP
Relax. Take a deep breathe. Now...

6y(x+3y)+9(x+3y)(x+3y)

(x+3y) - Common Factor.

6y(x+3y)+9(x+3y)(x+3y)

Now continue...
2. (Original post by TenOfThem)
Yes

What you have there is

6y(x+3y) + 9(x+3y)(x+3y)

Take out the red and what is left ... that is your other bracket
9y +9 + x
3. (Original post by zed963)
9y +9 + x
I am sorry but I am going to bow out now

You need to ask you teacher because you need someone sat next to you pointing to brackets, crossing things out, asking you questions

There is a major gap in your understanding here and you need someone to help properly

4. (Original post by Math12345)
Relax. Take a deep breathe. Now...

6y(x+3y)+9(x+3y)(x+3y)

(x+3y) - Common Factor.

6y(x+3y)+9(x+3y)(x+3y)

Now continue...
why have u crossed the 9 out
5. (Original post by zed963)
why have u crossed the 9 out
Look carefully.
6. (Original post by zed963)
9y +9 + x
6y(x+3y)+9(x+3y)(x+3y)

Remove the common factor I have crossed out and you are left with:

6y+9(x+3y)
6y+9x+27y

7. (Original post by zed963)
why have u crossed the 9 out

(Original post by Math12345)
Look carefully.
i thought the exact same thing, the 9 isn't crossed out, just how the 9 is displayed next to something that IS crossed out, makes it look like it is crossed out.

As TenOfThem said, you really need to go and see a teacher, or even ask a friend for some help. With these sort of things, you do need people to point it out to you, otherwise you'll just keep posting question after question.
8. (Original post by Math12345)
6y(x+3y)+9(x+3y)(x+3y)

Remove the common factor I have crossed out and you are left with:

6y+9(x+3y)
6y+9x+27y

So that would be 3(3x+11y)
9. (Original post by zed963)
So that would be 3(3x+11y)
Leave it as (9x+33y).
10. (Original post by zed963)
So that would be 3(3x+11y)
But in the answer sheet it give 3(x+y)(3x+11y)
11. (Original post by zed963)
But in the answer sheet it give 3(x+y)(3x+11y)
wouldn't matter. Either is correct.
12. (Original post by zed963)
But in the answer sheet it give 3(x+y)(3x+11y)
Talk to a teacher, because I don't think you get it completely.
13. (Original post by Math12345)
Talk to a teacher, because I don't think you get it completely.
but the common factor of 6 and 9 is three
14. (Original post by zed963)
but the common factor of 6 and 9 is three
Yes, but I still think you don't know how to get there.

Practice a few more questions.
15. (Original post by Math12345)
Yes, but I still think you don't know how to get there.

Practice a few more questions.
Have you got anymore questions?
16. (Original post by zed963)
Have you got anymore questions?
No, I suggest you ask your teacher first for a good detailed explanation then ask them for questions.
17. Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

16x^2 + 16x - 45

I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
18. Realised just now that this thread is marked as Secondary School maths so I'm going to try bumping it this one time and if that fails I'll make my own thread with the above question.
19. (Original post by Ronove)
Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

16x^2 + 16x - 45

I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
With those, I think you just have to 'see' it. Maybe someone has a better method (EDIT: Turns out Maths12345 does ), but if you can't see it then I'd just complete the square.
20. (Original post by Ronove)
Hi, I'm going to hijack this thread cos the topic is pretty similar. I'm self-teaching A-level and I unfortunately think I have missed something basic in factorising skills that keeps bringing me to a dead stop. It happens when the coefficient of x^2 is particularly high, especially when the resulting ac is large and negative. This is the problem that has just confused me at this point:

16x^2 + 16x - 45

I couldn't work out for the life of me any numbers that worked and when I checked the answer is (4x + 9)(4x - 5). I get that there was (probably?) a (16x + 36)(16x - 20) stage but I don't think I could ever have got to it by myself.

How do I go about finding the right figures? It's worst when b is positive and ac is negative, is there a method or a stage to the method I have missed to make it easier to figure out correctly? Thanks a lot for any help.
First thing to always check is if you can simplify the equation. In this case you can't.

16x^2+16x-45

The product is a*c: 16*-45=-720
The sum is b: +16

What 2 numbers give a product of -720 and a sum of +16?

36 and -20.

Now split the b term into this: (you should put it in a order, so you can factorise e.g. 16 and 36 (have 4 in common) and 20 and 45 (have 5 in common).

16x^2+36x-20x-45

Factorise

4x(4x+9)-5(4x+9)

Common factor?

(4x+9)

Next bracket is the bits left over.

(4x-5)

(4x+9)(4x-5)

## 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: April 15, 2012
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

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