(s^2-4)-81=0

Solution for (s^2-4)-81=0 equation:

(s^2-4)-81=0

We get rid of parentheses

s^2-4-81=0

We add all the numbers together, and all the variables

s^2-85=0

a = 1; b = 0; c = -85;
Δ = b2-4ac
Δ = 02-4·1·(-85)
Δ = 340
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{340}=\sqrt{4*85}=\sqrt{4}*\sqrt{85}=2\sqrt{85}$
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{85}}{2*1}=\frac{0-2\sqrt{85}}{2}
=-\frac{2\sqrt{85}}{2}
=-\sqrt{85}
$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{85}}{2*1}=\frac{0+2\sqrt{85}}{2}
=\frac{2\sqrt{85}}{2}
=\sqrt{85}
$