You are Here: Home >< Maths

# GCSE Further Maths question help watch

1. I'm just having a scroll through the June 2015 AQA Further Maths paper, and this one question has got me stumped:

In the expansion of the coefficient of is 0.

a) work out the value of k
b) work out the coefficient of x

On a solutions paper, the answers are a) k=-2 and b) -7; I'm not sure how this was worked out, due to the method being completely different to what I would use when expanding.

Could someone provide a small detailed explanation of how these results were obtained?

Thanks.
2. Did you multiply out the brackets?
3. You should get:
x^3 + kx^2 -3x + 2x^2 + 2kx - 6

When it says that the coefficient of x^2 is 0, it basically means the number in front of the x^2.
In the expression, you have kx^2 and 2x^2, and so k + 2 = 0. Therefore, k = -2
To get the coefficient of x, use the value of k that you just found. You have two values in the expression: -3x and 2kx
Since you know that k is -2, you can substitute thid in to get: -3x + (2*-2)x which simplifies to -7x.
So the coefficient of x is 7
Hope this helped! xx

EDIT: theholychilli
4. Also, to expand the brackets, multiply everything in the second set of brackets by x, and then everything in the second set of brackets by 2
5. (Original post by surina16)
You should get:
x^3 + kx^2 -3x + 2x^2 + 2kx - 6

When it says that the coefficient of x^2 is 0, it basically means the number in front of the x^2.
In the expression, you have kx^2 and 2x^2, and so k + 2 = 0. Therefore, k = -2
To get the coefficient of x, use the value of k that you just found. You have two values in the expression: -3x and 2kx
Since you know that k is -2, you can substitute thid in to get: -3x + (2*-2)x which simplifies to -7x.
So the coefficient of x is 7
Hope this helped! xx

EDIT: theholychilli
Much appreciated! Thanks, I was thinking that it would be (0x^2+kx-3) in the bracket and it didn't occur to me that it is after you have expanded it. Thanks!
6. (Original post by theholychilli)
Much appreciated! Thanks, I was thinking that it would be (0x^2+kx-3) in the bracket and it didn't occur to me that it is after you have expanded it. Thanks!
No problem!

### 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: February 23, 2016
The home of Results and Clearing

### 1,267

people online now

### 1,567,000

students helped last year
Today on TSR

### IT'S TODAY!

A-level results chat here

### University open days

1. London Metropolitan University
Sat, 18 Aug '18
2. Edge Hill University
Sat, 18 Aug '18
3. Bournemouth University
Sat, 18 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