(4x-16)(5x+7)=D

Solution for (4x-16)(5x+7)=D equation:

(4x-16)(5x+7)=

We move all terms to the left:

(4x-16)(5x+7)-()=0

We add all the numbers together, and all the variables

(4x-16)(5x+7)=0

We multiply parentheses ..

(+20x^2+28x-80x-112)=0

We get rid of parentheses

20x^2+28x-80x-112=0

We add all the numbers together, and all the variables

20x^2-52x-112=0

a = 20; b = -52; c = -112;
Δ = b2-4ac
Δ = -522-4·20·(-112)
Δ = 11664
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{11664}=108$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-52)-108}{2*20}=\frac{-56}{40}
=-1+2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-52)+108}{2*20}=\frac{160}{40}
=4
$