(2x-20)(5x+10)=0

Solution for (2x-20)(5x+10)=0 equation:

(2x-20)(5x+10)=0

We multiply parentheses ..

(+10x^2+20x-100x-200)=0

We get rid of parentheses

10x^2+20x-100x-200=0

We add all the numbers together, and all the variables

10x^2-80x-200=0

a = 10; b = -80; c = -200;
Δ = b2-4ac
Δ = -802-4·10·(-200)
Δ = 14400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{14400}=120$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-80)-120}{2*10}=\frac{-40}{20}
=-2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-80)+120}{2*10}=\frac{200}{20}
=10
$