a^2=18

Solution for a^2=18 equation:

a^2=18

We move all terms to the left:

a^2-(18)=0

a = 1; b = 0; c = -18;
Δ = b2-4ac
Δ = 02-4·1·(-18)
Δ = 72
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{72}=\sqrt{36*2}=\sqrt{36}*\sqrt{2}=6\sqrt{2}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{2}}{2*1}=\frac{0-6\sqrt{2}}{2}
=-\frac{6\sqrt{2}}{2}
=-3\sqrt{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{2}}{2*1}=\frac{0+6\sqrt{2}}{2}
=\frac{6\sqrt{2}}{2}
=3\sqrt{2}
$