You are Here: Home >< Maths

# How do I rearrange this ? watch

1. (Original post by eliotball)
No problem, I'm sure you had good intentions posting that solution, it was just a pretty awful mistake :P
Um yeah, big mistake! I feel stupid now, haha.
2. (Original post by kingkongjaffa)
thanks how do you come to that? I'm not very good at factorising with things that have coefficients of x :P
You have to think that you have

3x^2 -10x +7 = 0

So something x times x gives 3x^2, so that something can only be 3. That gives you a starting point with two numbers that are unknown (we'll call them a and b)
(3x + a)(x + b)= 0
You also know that if you seperate out this bracket (which I am sure you can do)
You get...
3x^2 + ax + 3bx + ab = 0

So a times be has to be 7. Leaves you with a choice of 1, -1, 7 and -7 for a and b.
You also know that ax + 3bx is -10x, so then you know that a + b is -10. There is only one solution of the a and bs that we have shown will work.

Hope that helps!
3. (Original post by birduk)
You have to think that you have

3x^2 -10x +7 = 0

So something x times x gives 3x^2, so that something can only be 3. That gives you a starting point with two numbers that are unknown (we'll call them a and b)
(3x + a)(x + b)= 0
You also know that if you seperate out this bracket (which I am sure you can do)
You get...
3x^2 + ax + 3bx + ab = 0

So a times be has to be 7. Leaves you with a choice of 1, -1, 7 and -7 for a and b.
You also know that ax + 3bx is -10x, so then you know that a + b is -10. There is only one solution of the a and bs that we have shown will work.

Hope that helps!
thanks a lot
4. (Original post by kingkongjaffa)
ooh can you explain this please firstly AC is 3*7 but can you explain why you did that.
secondly can you explain how you go from 3x(x-1) -7(x-1) to (3x-7) (x-1)?
Well because the co-efficient of x^2 is greater than two, you must multiply the co-efficient of x^2 by the constant which is A x C ( if confused as to the letters, remember the quadratic equation).

You go from 3x(x-1) -7(x-1) to (3x-7) (x-1) by eliminating one (x-1) and making the numbers outside each bracket into another bracket. REMEMBER to eliminate one bracket, both brackets have to be the same.....

eg: 4x(x+5) 5(x+5) will become (4x +5)(x+5)

and, 11x(x-3) -4(x-3) = (11x-4)(x-3)

Note the Solutions for x exist when you make the bracket equal to 0...

eg (4x + 5)(x+5) =0

4x+5=0
4x= -5
x= -5/4

and, x +5 = 0
x = -5
5. (Original post by Tizmo)
Um yeah, big mistake! I feel stupid now, haha.
The feeling will wear off
6. (Original post by crazycake93)
Well because the co-efficient of x^2 is greater than two, you must multiply the co-efficient of x^2 by the constant which is A x C ( if confused as to the letters, remember the quadratic equation).

You go from 3x(x-1) -7(x-1) to (3x-7) (x-1) by eliminating one (x-1) and making the numbers outside each bracket into another bracket. REMEMBER to eliminate one bracket, both brackets have to be the same.....

eg: 4x(x+5) 5(x+5) will become (4x +5)(x+5)

and, 11x(x-3) -4(x-3) = (11x-4)(x-3)

Note the Solutions for x exist when you make the bracket equal to 0...

eg (4x + 5)(x+5) =0

4x+5=0
4x= -5
x= -5/4

and, x +5 = 0
x = -5

Thanks i understand it now the examples helped aswell thanks for taking the time to read the thread, all of you.
7. Hire a removal firm?

### 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: March 21, 2011
Today on TSR

How do you think you'll do?

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
Poll
Useful resources

### 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