4d^2-26d-20=0

Solution for 4d^2-26d-20=0 equation:

4d^2-26d-20=0

a = 4; b = -26; c = -20;
Δ = b2-4ac
Δ = -262-4·4·(-20)
Δ = 996
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:

$\sqrt{\Delta}=\sqrt{996}=\sqrt{4*249}=\sqrt{4}*\sqrt{249}=2\sqrt{249}$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-2\sqrt{249}}{2*4}=\frac{26-2\sqrt{249}}{8}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+2\sqrt{249}}{2*4}=\frac{26+2\sqrt{249}}{8}
$