-y(y-18)=-18

Solution for -y(y-18)=-18 equation:

-y(y-18)=-18

We move all terms to the left:

-y(y-18)-(-18)=0

We add all the numbers together, and all the variables

-y(y-18)+18=0

We multiply parentheses

-y^2+18y+18=0

We add all the numbers together, and all the variables

-1y^2+18y+18=0

a = -1; b = 18; c = +18;
Δ = b2-4ac
Δ = 182-4·(-1)·18
Δ = 396
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{396}=\sqrt{36*11}=\sqrt{36}*\sqrt{11}=6\sqrt{11}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-6\sqrt{11}}{2*-1}=\frac{-18-6\sqrt{11}}{-2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+6\sqrt{11}}{2*-1}=\frac{-18+6\sqrt{11}}{-2}
$