H=-5t^2+90t

Solution for H=-5t^2+90t equation:

=-5H^2+90H

We move all terms to the left:

-(-5H^2+90H)=0

We get rid of parentheses

5H^2-90H=0

a = 5; b = -90; c = 0;
Δ = b2-4ac
Δ = -902-4·5·0
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-90)-90}{2*5}=\frac{0}{10}
=0
$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-90)+90}{2*5}=\frac{180}{10}
=18
$