(-2x+20)(-2x+30)=0

Solution for (-2x+20)(-2x+30)=0 equation:

(-2x+20)(-2x+30)=0

We multiply parentheses ..

(+4x^2-60x-40x+600)=0

We get rid of parentheses

4x^2-60x-40x+600=0

We add all the numbers together, and all the variables

4x^2-100x+600=0

a = 4; b = -100; c = +600;
Δ = b2-4ac
Δ = -1002-4·4·600
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-100)-20}{2*4}=\frac{80}{8}
=10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-100)+20}{2*4}=\frac{120}{8}
=15
$