# Root Difference

• September 30th 2008, 05:13 AM
Logic
Root Difference
Greetings,

While I was in the library once, I've seen a neat trick for finding the difference of the roots of a quadratic equation, x2 - x1 that is. Most unfortunately, I have failed to recall it and cannot think of any other way to do it. Except finding the roots and then subtracting, but that is not quite an interesting thing to do, especially, when the equation is rather complex...
I would appreciate some hints.

Thank you.
• September 30th 2008, 05:46 AM
TKHunny
I don't know how "neat" it is, but you could take the two results of the quadratic formula and simply subtract them.
• September 30th 2008, 10:48 PM
Logic
It doesn't appear a good solution to me, because the equation I have is:
$x^2-2(m+1)x-m^2-2m-2$

and I am looking for what m x2-x1 equals 6.

The "neat" trick I think was realised using the Viet's formulae. Vieth or Wieth - could figure out the correct spelling, sorry...

It was like mixing the two x2-x1 and x1+x2, but, ah, ok - I don't really know....