(x+20)(x-4)=476

Solution for (x+20)(x-4)=476 equation:

(x+20)(x-4)=476

We move all terms to the left:

(x+20)(x-4)-(476)=0

We multiply parentheses ..

(+x^2-4x+20x-80)-476=0

We get rid of parentheses

x^2-4x+20x-80-476=0

We add all the numbers together, and all the variables

x^2+16x-556=0

a = 1; b = 16; c = -556;
Δ = b2-4ac
Δ = 162-4·1·(-556)
Δ = 2480
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{2480}=\sqrt{16*155}=\sqrt{16}*\sqrt{155}=4\sqrt{155}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-4\sqrt{155}}{2*1}=\frac{-16-4\sqrt{155}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+4\sqrt{155}}{2*1}=\frac{-16+4\sqrt{155}}{2}
$