H=-0.8d^2+0.8d+1.6

Solution for H=-0.8d^2+0.8d+1.6 equation:

=-0.8H^2+0.8H+1.6

We move all terms to the left:

-(-0.8H^2+0.8H+1.6)=0

We get rid of parentheses

0.8H^2-0.8H-1.6=0

a = 0.8; b = -0.8; c = -1.6;
Δ = b2-4ac
Δ = -0.82-4·0.8·(-1.6)
Δ = 5.76
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.8)-\sqrt{5.76}}{2*0.8}=\frac{0.8-\sqrt{5.76}}{1.6}
$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.8)+\sqrt{5.76}}{2*0.8}=\frac{0.8+\sqrt{5.76}}{1.6}
$