(4x-8)(x+7)=0

Solution for (4x-8)(x+7)=0 equation:

(4x-8)(x+7)=0

We multiply parentheses ..

(+4x^2+28x-8x-56)=0

We get rid of parentheses

4x^2+28x-8x-56=0

We add all the numbers together, and all the variables

4x^2+20x-56=0

a = 4; b = 20; c = -56;
Δ = b2-4ac
Δ = 202-4·4·(-56)
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-36}{2*4}=\frac{-56}{8}
=-7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+36}{2*4}=\frac{16}{8}
=2
$