-5(x+1)(x-3)=0

Solution for -5(x+1)(x-3)=0 equation:

-5(x+1)(x-3)=0

We multiply parentheses ..

-5(+x^2-3x+x-3)=0

We multiply parentheses

-5x^2+15x-5x+15=0

We add all the numbers together, and all the variables

-5x^2+10x+15=0

a = -5; b = 10; c = +15;
Δ = b2-4ac
Δ = 102-4·(-5)·15
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-20}{2*-5}=\frac{-30}{-10}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+20}{2*-5}=\frac{10}{-10}
=-1
$