4d2-25d-20=0

Solution for 4d2-25d-20=0 equation:

4d^2-25d-20=0

a = 4; b = -25; c = -20;
Δ = b2-4ac
Δ = -252-4·4·(-20)
Δ = 945
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:

$\sqrt{\Delta}=\sqrt{945}=\sqrt{9*105}=\sqrt{9}*\sqrt{105}=3\sqrt{105}$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-3\sqrt{105}}{2*4}=\frac{25-3\sqrt{105}}{8}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+3\sqrt{105}}{2*4}=\frac{25+3\sqrt{105}}{8}
$