(X+4)(x-9)=O

Solution for (X+4)(x-9)=O equation:

(X+4)(X-9)=

We move all terms to the left:

(X+4)(X-9)-()=0

We add all the numbers together, and all the variables

(X+4)(X-9)=0

We multiply parentheses ..

(+X^2-9X+4X-36)=0

We get rid of parentheses

X^2-9X+4X-36=0

We add all the numbers together, and all the variables

X^2-5X-36=0

a = 1; b = -5; c = -36;
Δ = b2-4ac
Δ = -52-4·1·(-36)
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-13}{2*1}=\frac{-8}{2}
=-4
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+13}{2*1}=\frac{18}{2}
=9
$