You are Here: Home >< Maths

# simultaneous equation by substitution watch

1. i kind of stuck on this question.

y = 3x
2y^2 - xy = 15

I substitute the y value in the second equation and after expanding i dont get any x's just x^2.

2(3x)^2 - x(3x) = 15
18x^2 - 3x^2 = 15
15x^2 = 15
15x^2 - 15 = 0

So im stuck at that point.
2. Divide by 15 and factorise by using the difference of two squares or just solve x^2 = ? (remember two answers).

### 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: October 3, 2010
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