(2x+8)(x-9)=0

Solution for (2x+8)(x-9)=0 equation:

(2x+8)(x-9)=0

We multiply parentheses ..

(+2x^2-18x+8x-72)=0

We get rid of parentheses

2x^2-18x+8x-72=0

We add all the numbers together, and all the variables

2x^2-10x-72=0

a = 2; b = -10; c = -72;
Δ = b2-4ac
Δ = -102-4·2·(-72)
Δ = 676
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{676}=26$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-26}{2*2}=\frac{-16}{4}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+26}{2*2}=\frac{36}{4}
=9
$