(X+7)(x-5)=-20

Solution for (X+7)(x-5)=-20 equation:

(X+7)(X-5)=-20

We move all terms to the left:

(X+7)(X-5)-(-20)=0

We add all the numbers together, and all the variables

(X+7)(X-5)+20=0

We multiply parentheses ..

(+X^2-5X+7X-35)+20=0

We get rid of parentheses

X^2-5X+7X-35+20=0

We add all the numbers together, and all the variables

X^2+2X-15=0

a = 1; b = 2; c = -15;
Δ = b2-4ac
Δ = 22-4·1·(-15)
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-8}{2*1}=\frac{-10}{2}
=-5
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+8}{2*1}=\frac{6}{2}
=3
$