D(x)=-x^2+12x+4

Solution for D(x)=-x^2+12x+4 equation:

(D)=-D^2+12D+4

We move all terms to the left:

(D)-(-D^2+12D+4)=0

We get rid of parentheses

D^2-12D+D-4=0

We add all the numbers together, and all the variables

D^2-11D-4=0

a = 1; b = -11; c = -4;
Δ = b2-4ac
Δ = -112-4·1·(-4)
Δ = 137
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$D_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$D_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$D_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-11)-\sqrt{137}}{2*1}=\frac{11-\sqrt{137}}{2}
$
$D_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-11)+\sqrt{137}}{2*1}=\frac{11+\sqrt{137}}{2}
$