(x+20)(2x-28)=0

Solution for (x+20)(2x-28)=0 equation:

(x+20)(2x-28)=0

We multiply parentheses ..

(+2x^2-28x+40x-560)=0

We get rid of parentheses

2x^2-28x+40x-560=0

We add all the numbers together, and all the variables

2x^2+12x-560=0

a = 2; b = 12; c = -560;
Δ = b2-4ac
Δ = 122-4·2·(-560)
Δ = 4624
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4624}=68$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-68}{2*2}=\frac{-80}{4}
=-20
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+68}{2*2}=\frac{56}{4}
=14
$