(X-12)(x+28)=0

Solution for (X-12)(x+28)=0 equation:

(X-12)(X+28)=0

We multiply parentheses ..

(+X^2+28X-12X-336)=0

We get rid of parentheses

X^2+28X-12X-336=0

We add all the numbers together, and all the variables

X^2+16X-336=0

a = 1; b = 16; c = -336;
Δ = b2-4ac
Δ = 162-4·1·(-336)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-40}{2*1}=\frac{-56}{2}
=-28
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+40}{2*1}=\frac{24}{2}
=12
$