Originally Posted by

**AshleyT** Sorry if this is in the wrong section. I wasn't sure where it went!

If you have an equation:

$\displaystyle

x^2 + 4x + 7 = 0

$

Which has roots

$\displaystyle \alpha and \beta$

And you want an equation that has roots

$\displaystyle

\alpha + 2\beta and \beta + 2\alpha

$

How would you go about this by substitution? Because if i do

$\displaystyle let u = \alpha + 2\beta$

Im going to get alpha in terms of beta and u...and if i sub this into the equation im going to still have beta :S...

I know you can do it via sum of roots = -b/a etc but im told in this example to use substitution -,-.

Thanks.