# Factoring with the quadratic formula

1. Oct 1, 2006

### Checkfate

I have a huge headache and I can't understand why this works... I am reviewing the quadratic formula so that I can solve trig questions, but I am stuck on this one part...

The point is to factor $$x^2+2x-1$$

I ( and the textbook ) use the quadratic formula to get the roots of it and come up with

$$-1\pm\sqrt{2}$$

How do I use this to factor into $$(x+1-\sqrt{2})(x+1+\sqrt{2})$$?

I remember the quadratic formula as being more useful for solving quadratics where 1 side =0... I don't remember factoring with it! Can someone help? I would try to figure it out on my own but my head is spinning and I am under time pressure at this point. Thanks alot guys.

I really do appreciate the help that I recieve on these boards.

Last edited: Oct 1, 2006
2. Oct 1, 2006

### Integral

Staff Emeritus
The quadratic formula gives you 2 roots r1 and r2 you then get the factors from

(x - r1) (x - r2) You then need to check your work by multiplying the 2 factors to ensure that you get back your starting quadratic.

3. Oct 2, 2006

### Checkfate

Thankyou Integral!! You helped me remember :)