A=-2x^2+72x

Solution for A=-2x^2+72x equation:

=-2A^2+72A

We move all terms to the left:

-(-2A^2+72A)=0

We get rid of parentheses

2A^2-72A=0

a = 2; b = -72; c = 0;
Δ = b2-4ac
Δ = -722-4·2·0
Δ = 5184
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5184}=72$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-72)-72}{2*2}=\frac{0}{4}
=0
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-72)+72}{2*2}=\frac{144}{4}
=36
$