5=(3x^2)+15x

Solution for 5=(3x^2)+15x equation:

5=(3x^2)+15x

We move all terms to the left:

5-((3x^2)+15x)=0

We get rid of parentheses

-3x^2-15x+5=0

a = -3; b = -15; c = +5;
Δ = b2-4ac
Δ = -152-4·(-3)·5
Δ = 285
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-\sqrt{285}}{2*-3}=\frac{15-\sqrt{285}}{-6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{285}}{2*-3}=\frac{15+\sqrt{285}}{-6}
$