d^2-19.5d+58.5=0

Solution for d^2-19.5d+58.5=0 equation:

d^2-19.5d+58.5=0

a = 1; b = -19.5; c = +58.5;
Δ = b2-4ac
Δ = -19.52-4·1·58.5
Δ = 146.25
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{-(-19.5)-\sqrt{146.25}}{2*1}=\frac{19.5-\sqrt{146.25}}{2}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-19.5)+\sqrt{146.25}}{2*1}=\frac{19.5+\sqrt{146.25}}{2}
$