(X+4)(x-5)=20

Solution for (X+4)(x-5)=20 equation:

(X+4)(X-5)=20

We move all terms to the left:

(X+4)(X-5)-(20)=0

We multiply parentheses ..

(+X^2-5X+4X-20)-20=0

We get rid of parentheses

X^2-5X+4X-20-20=0

We add all the numbers together, and all the variables

X^2-1X-40=0

a = 1; b = -1; c = -40;
Δ = b2-4ac
Δ = -12-4·1·(-40)
Δ = 161
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-\sqrt{161}}{2*1}=\frac{1-\sqrt{161}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{161}}{2*1}=\frac{1+\sqrt{161}}{2}
$