18=y^2-12

Solution for 18=y^2-12 equation:

18=y^2-12

We move all terms to the left:

18-(y^2-12)=0

We get rid of parentheses

-y^2+12+18=0

We add all the numbers together, and all the variables

-1y^2+30=0

a = -1; b = 0; c = +30;
Δ = b2-4ac
Δ = 02-4·(-1)·30
Δ = 120
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{120}=\sqrt{4*30}=\sqrt{4}*\sqrt{30}=2\sqrt{30}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{30}}{2*-1}=\frac{0-2\sqrt{30}}{-2}
=-\frac{2\sqrt{30}}{-2}
=-\frac{\sqrt{30}}{-1}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{30}}{2*-1}=\frac{0+2\sqrt{30}}{-2}
=\frac{2\sqrt{30}}{-2}
=\frac{\sqrt{30}}{-1}
$