4(2-x)(x+7)=0

Solution for 4(2-x)(x+7)=0 equation:

4(2-x)(x+7)=0

We add all the numbers together, and all the variables

4(-1x+2)(x+7)=0

We multiply parentheses ..

4(-1x^2-7x+2x+14)=0

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