-2n(n+10)=-28

Solution for -2n(n+10)=-28 equation:

-2n(n+10)=-28

We move all terms to the left:

-2n(n+10)-(-28)=0

We add all the numbers together, and all the variables

-2n(n+10)+28=0

We multiply parentheses

-2n^2-20n+28=0

a = -2; b = -20; c = +28;
Δ = b2-4ac
Δ = -202-4·(-2)·28
Δ = 624
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{624}=\sqrt{16*39}=\sqrt{16}*\sqrt{39}=4\sqrt{39}$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-4\sqrt{39}}{2*-2}=\frac{20-4\sqrt{39}}{-4}
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+4\sqrt{39}}{2*-2}=\frac{20+4\sqrt{39}}{-4}
$