2x(x-18)=90

Solution for 2x(x-18)=90 equation:

2x(x-18)=90

We move all terms to the left:

2x(x-18)-(90)=0

We multiply parentheses

2x^2-36x-90=0

a = 2; b = -36; c = -90;
Δ = b2-4ac
Δ = -362-4·2·(-90)
Δ = 2016
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:

$\sqrt{\Delta}=\sqrt{2016}=\sqrt{144*14}=\sqrt{144}*\sqrt{14}=12\sqrt{14}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-36)-12\sqrt{14}}{2*2}=\frac{36-12\sqrt{14}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-36)+12\sqrt{14}}{2*2}=\frac{36+12\sqrt{14}}{4}
$