(15-2x)(20-2x)=0

Solution for (15-2x)(20-2x)=0 equation:

(15-2x)(20-2x)=0

We add all the numbers together, and all the variables

(-2x+15)(-2x+20)=0

We multiply parentheses ..

(+4x^2-40x-30x+300)=0

We get rid of parentheses

4x^2-40x-30x+300=0

We add all the numbers together, and all the variables

4x^2-70x+300=0

a = 4; b = -70; c = +300;
Δ = b2-4ac
Δ = -702-4·4·300
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-70)-10}{2*4}=\frac{60}{8}
=7+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-70)+10}{2*4}=\frac{80}{8}
=10
$