(x-6)(x-6)=20

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

(x-6)(x-6)=20

We move all terms to the left:

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

We multiply parentheses ..

(+x^2-6x-6x+36)-20=0

We get rid of parentheses

x^2-6x-6x+36-20=0

We add all the numbers together, and all the variables

x^2-12x+16=0

a = 1; b = -12; c = +16;
Δ = b2-4ac
Δ = -122-4·1·16
Δ = 80
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{80}=\sqrt{16*5}=\sqrt{16}*\sqrt{5}=4\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-4\sqrt{5}}{2*1}=\frac{12-4\sqrt{5}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+4\sqrt{5}}{2*1}=\frac{12+4\sqrt{5}}{2}
$