(10x-10)(x+9)=0

Solution for (10x-10)(x+9)=0 equation:

(10x-10)(x+9)=0

We multiply parentheses ..

(+10x^2+90x-10x-90)=0

We get rid of parentheses

10x^2+90x-10x-90=0

We add all the numbers together, and all the variables

10x^2+80x-90=0

a = 10; b = 80; c = -90;
Δ = b2-4ac
Δ = 802-4·10·(-90)
Δ = 10000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{10000}=100$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-100}{2*10}=\frac{-180}{20}
=-9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+100}{2*10}=\frac{20}{20}
=1
$