(x+7)(2x-20)=0

Solution for (x+7)(2x-20)=0 equation:

(x+7)(2x-20)=0

We multiply parentheses ..

(+2x^2-20x+14x-140)=0

We get rid of parentheses

2x^2-20x+14x-140=0

We add all the numbers together, and all the variables

2x^2-6x-140=0

a = 2; b = -6; c = -140;
Δ = b2-4ac
Δ = -62-4·2·(-140)
Δ = 1156
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1156}=34$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-34}{2*2}=\frac{-28}{4}
=-7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+34}{2*2}=\frac{40}{4}
=10
$