0=-5x^2+36x+81

Solution for 0=-5x^2+36x+81 equation:

0=-5x^2+36x+81

We move all terms to the left:

0-(-5x^2+36x+81)=0

We add all the numbers together, and all the variables

-(-5x^2+36x+81)=0

We get rid of parentheses

5x^2-36x-81=0

a = 5; b = -36; c = -81;
Δ = b2-4ac
Δ = -362-4·5·(-81)
Δ = 2916
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2916}=54$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-36)-54}{2*5}=\frac{-18}{10}
=-1+4/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-36)+54}{2*5}=\frac{90}{10}
=9
$