2x(x/2-21)=180

Solution for 2x(x/2-21)=180 equation:

2x(x/2-21)=180

We move all terms to the left:

2x(x/2-21)-(180)=0

We multiply parentheses

2x^2-42x-180=0

a = 2; b = -42; c = -180;
Δ = b2-4ac
Δ = -422-4·2·(-180)
Δ = 3204
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:

$\sqrt{\Delta}=\sqrt{3204}=\sqrt{36*89}=\sqrt{36}*\sqrt{89}=6\sqrt{89}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-42)-6\sqrt{89}}{2*2}=\frac{42-6\sqrt{89}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-42)+6\sqrt{89}}{2*2}=\frac{42+6\sqrt{89}}{4}
$