-5(x+1)(x-9)=0

Solution for -5(x+1)(x-9)=0 equation:

-5(x+1)(x-9)=0

We multiply parentheses ..

-5(+x^2-9x+x-9)=0

We multiply parentheses

-5x^2+45x-5x+45=0

We add all the numbers together, and all the variables

-5x^2+40x+45=0

a = -5; b = 40; c = +45;
Δ = b2-4ac
Δ = 402-4·(-5)·45
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(40)-50}{2*-5}=\frac{-90}{-10}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(40)+50}{2*-5}=\frac{10}{-10}
=-1
$