d(d+2)=1120

Solution for d(d+2)=1120 equation:

d(d+2)=1120

We move all terms to the left:

d(d+2)-(1120)=0

We multiply parentheses

d^2+2d-1120=0

a = 1; b = 2; c = -1120;
Δ = b2-4ac
Δ = 22-4·1·(-1120)
Δ = 4484
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:

$\sqrt{\Delta}=\sqrt{4484}=\sqrt{4*1121}=\sqrt{4}*\sqrt{1121}=2\sqrt{1121}$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{1121}}{2*1}=\frac{-2-2\sqrt{1121}}{2}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{1121}}{2*1}=\frac{-2+2\sqrt{1121}}{2}
$