-5-4b^2=-81

Solution for -5-4b^2=-81 equation:

-5-4b^2=-81

We move all terms to the left:

-5-4b^2-(-81)=0

We add all the numbers together, and all the variables

-4b^2+76=0

a = -4; b = 0; c = +76;
Δ = b2-4ac
Δ = 02-4·(-4)·76
Δ = 1216
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1216}=\sqrt{64*19}=\sqrt{64}*\sqrt{19}=8\sqrt{19}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-8\sqrt{19}}{2*-4}=\frac{0-8\sqrt{19}}{-8}
=-\frac{8\sqrt{19}}{-8}
=-\frac{\sqrt{19}}{-1}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+8\sqrt{19}}{2*-4}=\frac{0+8\sqrt{19}}{-8}
=\frac{8\sqrt{19}}{-8}
=\frac{\sqrt{19}}{-1}
$