-4d^2+36d+81=0

Solution for -4d^2+36d+81=0 equation:

-4d^2+36d+81=0

a = -4; b = 36; c = +81;
Δ = b2-4ac
Δ = 362-4·(-4)·81
Δ = 2592
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{2592}=\sqrt{1296*2}=\sqrt{1296}*\sqrt{2}=36\sqrt{2}$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(36)-36\sqrt{2}}{2*-4}=\frac{-36-36\sqrt{2}}{-8}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(36)+36\sqrt{2}}{2*-4}=\frac{-36+36\sqrt{2}}{-8}
$