-5x-15=5x(x+3)

Solution for -5x-15=5x(x+3) equation:

-5x-15=5x(x+3)

We move all terms to the left:

-5x-15-(5x(x+3))=0


We calculate terms in parentheses: -(5x(x+3)), so:

5x(x+3)

We multiply parentheses

5x^2+15x

Back to the equation:

-(5x^2+15x)


We get rid of parentheses

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

We add all the numbers together, and all the variables

-5x^2-20x-15=0

a = -5; b = -20; c = -15;
Δ = b2-4ac
Δ = -202-4·(-5)·(-15)
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-10}{2*-5}=\frac{10}{-10}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+10}{2*-5}=\frac{30}{-10}
=-3
$