(X-6)(x-20)=0

Solution for (X-6)(x-20)=0 equation:

(X-6)(X-20)=0

We multiply parentheses ..

(+X^2-20X-6X+120)=0

We get rid of parentheses

X^2-20X-6X+120=0

We add all the numbers together, and all the variables

X^2-26X+120=0

a = 1; b = -26; c = +120;
Δ = b2-4ac
Δ = -262-4·1·120
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-14}{2*1}=\frac{12}{2}
=6
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+14}{2*1}=\frac{40}{2}
=20
$