You are Here: Home >< Maths

# Simple but amazingly hard quadratic- can't factorise! watch

Announcements
1. I'm doing a workbook before my first ever maths lecture tomorrow, and I can't factorise this quadratic! :O

x squared minus x minus 1

The solution is (x-0.5(1-sqrt 5))(x-0.5(1+sqrt 5 ))

I've never factorised a quadratic that has had a similar answer before, but I notice that it has something to do with taking advantage of:

a^2 + b^2 = (a+b)(a-b)

What is the method for solving these quadratics, and when do you know how to use this method?

Thanks guys im in a bit of a jam here :/
2. (Original post by joelio36)
I'm doing a workbook before my first ever maths lecture tomorrow, and I can't factorise this quadratic! :O

x squared minus x minus 1

The solution is (x-0.5(1-sqrt 5))(x-0.5(1+sqrt 5 ))

I've never factorised a quadratic that has had a similar answer before, but I notice that it has something to do with taking advantage of:

a^2 + b^2 = (a+b)(a-b)

What is the method for solving these quadratics, and when do you know how to use this method?

Thanks guys im in a bit of a jam here :/
NB it is minus and not plus as you have written.

Is it
3. Use the quadratic formula after you have x(sqrt) - x - 1
5. uh a^2-b^2=(a+b)(a-b)
aka difference of two squares.

For this example use the quadratic formula to find the roots and then you know that (x-r_1)(x-r_2) will give you your quadratic where r_n is a root.
6. Cheers guys i got it now

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 9, 2009
Today on TSR

### Official 2019 Cambridge Interview Thread

Discuss upcoming interviews...

### University open days

• Heriot-Watt University
School of Textiles and Design Undergraduate
Fri, 16 Nov '18
• University of Roehampton
Sat, 17 Nov '18
• Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 17 Nov '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