I created my first simple extension (for testing). 
I have seen this extension: [Extension] Math Formulas [V3]
Yes, this returns x1, which of course can also be negative. But what about x2 ?
I used the Extension Template Repository: Extension Template Repository
(of course, not a big deal, but for the first time)
de.BodyMindPower.quadraticEquation.aix (5.6 KB)
UPDATE v2: de.BodyMindPower.quadraticEquation_v2.aix (5.7 KB)
I have simplified the extension following @vishwas advice:
