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

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

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

We move all terms to the left:

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

We get rid of parentheses

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

We multiply parentheses ..

(+x^2+5x-4x-20)+7x=0

We get rid of parentheses

x^2+5x-4x+7x-20=0

We add all the numbers together, and all the variables

x^2+8x-20=0

a = 1; b = 8; c = -20;
Δ = b2-4ac
Δ = 82-4·1·(-20)
Δ = 144
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{144}=12$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-12}{2*1}=\frac{-20}{2}
=-10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+12}{2*1}=\frac{4}{2}
=2
$