0=3x^2+12x-15

Solution for 0=3x^2+12x-15 equation:

0=3x^2+12x-15

We move all terms to the left:

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

We add all the numbers together, and all the variables

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

We get rid of parentheses

-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
$