90=9x^2

Solution for 90=9x^2 equation:

90=9x^2

We move all terms to the left:

90-(9x^2)=0

a = -9; b = 0; c = +90;
Δ = b2-4ac
Δ = 02-4·(-9)·90
Δ = 3240
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:

$\sqrt{\Delta}=\sqrt{3240}=\sqrt{324*10}=\sqrt{324}*\sqrt{10}=18\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18\sqrt{10}}{2*-9}=\frac{0-18\sqrt{10}}{-18}
=-\frac{18\sqrt{10}}{-18}
=-\frac{\sqrt{10}}{-1}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18\sqrt{10}}{2*-9}=\frac{0+18\sqrt{10}}{-18}
=\frac{18\sqrt{10}}{-18}
=\frac{\sqrt{10}}{-1}
$