-r^2-28r-20=0

Solution for -r^2-28r-20=0 equation:

-r^2-28r-20=0

We add all the numbers together, and all the variables

-1r^2-28r-20=0

a = -1; b = -28; c = -20;
Δ = b2-4ac
Δ = -282-4·(-1)·(-20)
Δ = 704
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{704}=\sqrt{64*11}=\sqrt{64}*\sqrt{11}=8\sqrt{11}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-8\sqrt{11}}{2*-1}=\frac{28-8\sqrt{11}}{-2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+8\sqrt{11}}{2*-1}=\frac{28+8\sqrt{11}}{-2}
$