90=2h^2+10h

Solution for 90=2h^2+10h equation:

90=2h^2+10h

We move all terms to the left:

90-(2h^2+10h)=0

We get rid of parentheses

-2h^2-10h+90=0

a = -2; b = -10; c = +90;
Δ = b2-4ac
Δ = -102-4·(-2)·90
Δ = 820
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{820}=\sqrt{4*205}=\sqrt{4}*\sqrt{205}=2\sqrt{205}$
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-2\sqrt{205}}{2*-2}=\frac{10-2\sqrt{205}}{-4}
$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+2\sqrt{205}}{2*-2}=\frac{10+2\sqrt{205}}{-4}
$