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

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

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

We multiply parentheses ..

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

We get rid of parentheses

2x^2-8x+18x-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{-36}{4}
=-9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+26}{2*2}=\frac{16}{4}
=4
$