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

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

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

We move all terms to the left:

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


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

3(x+5)3x

We multiply parentheses

9x^2+45x

Back to the equation:

-(9x^2+45x)


We get rid of parentheses

-9x^2+3x-45x+15=0

We add all the numbers together, and all the variables

-9x^2-42x+15=0

a = -9; b = -42; c = +15;
Δ = b2-4ac
Δ = -422-4·(-9)·15
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-42)-48}{2*-9}=\frac{-6}{-18}
=1/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-42)+48}{2*-9}=\frac{90}{-18}
=-5
$