120=15x^2-5

Solution for 120=15x^2-5 equation:

120=15x^2-5

We move all terms to the left:

120-(15x^2-5)=0

We get rid of parentheses

-15x^2+5+120=0

We add all the numbers together, and all the variables

-15x^2+125=0

a = -15; b = 0; c = +125;
Δ = b2-4ac
Δ = 02-4·(-15)·125
Δ = 7500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{7500}=\sqrt{2500*3}=\sqrt{2500}*\sqrt{3}=50\sqrt{3}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-50\sqrt{3}}{2*-15}=\frac{0-50\sqrt{3}}{-30}
=-\frac{50\sqrt{3}}{-30}
=-\frac{5\sqrt{3}}{-3}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+50\sqrt{3}}{2*-15}=\frac{0+50\sqrt{3}}{-30}
=\frac{50\sqrt{3}}{-30}
=\frac{5\sqrt{3}}{-3}
$