d^2-84=5d

Solution for d^2-84=5d equation:

d^2-84=5d

We move all terms to the left:

d^2-84-(5d)=0

a = 1; b = -5; c = -84;
Δ = b2-4ac
Δ = -52-4·1·(-84)
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-19}{2*1}=\frac{-14}{2}
=-7
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+19}{2*1}=\frac{24}{2}
=12
$