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

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

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

We move all terms to the left:

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


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

3(x+5)x

We multiply parentheses

3x^2+15x

Back to the equation:

-(3x^2+15x)


We get rid of parentheses

-3x^2+3x-15x+15=0

We add all the numbers together, and all the variables

-3x^2-12x+15=0

a = -3; b = -12; c = +15;
Δ = b2-4ac
Δ = -122-4·(-3)·15
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-18}{2*-3}=\frac{-6}{-6}
=1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+18}{2*-3}=\frac{30}{-6}
=-5
$