(X-2)(x+20)=0

Solution for (X-2)(x+20)=0 equation:

(X-2)(X+20)=0

We multiply parentheses ..

(+X^2+20X-2X-40)=0

We get rid of parentheses

X^2+20X-2X-40=0

We add all the numbers together, and all the variables

X^2+18X-40=0

a = 1; b = 18; c = -40;
Δ = b2-4ac
Δ = 182-4·1·(-40)
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-22}{2*1}=\frac{-40}{2}
=-20
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+22}{2*1}=\frac{4}{2}
=2
$