0=12x-3x(x+9)

Solution for 0=12x-3x(x+9) equation:

0=12x-3x(x+9)

We move all terms to the left:

0-(12x-3x(x+9))=0

We add all the numbers together, and all the variables

-(12x-3x(x+9))=0


We calculate terms in parentheses: -(12x-3x(x+9)), so:

12x-3x(x+9)

We multiply parentheses

-3x^2+12x-27x

We add all the numbers together, and all the variables

-3x^2-15x

Back to the equation:

-(-3x^2-15x)


We get rid of parentheses

3x^2+15x=0

a = 3; b = 15; c = 0;
Δ = b2-4ac
Δ = 152-4·3·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-15}{2*3}=\frac{-30}{6}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+15}{2*3}=\frac{0}{6}
=0
$