81^4=x^2

Solution for 81^4=x^2 equation:

81^4=x^2

We move all terms to the left:

81^4-(x^2)=0

We add all the numbers together, and all the variables

-1x^2+43046721=0

a = -1; b = 0; c = +43046721;
Δ = b2-4ac
Δ = 02-4·(-1)·43046721
Δ = 172186884
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{172186884}=13122$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-13122}{2*-1}=\frac{-13122}{-2}
=+6561
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+13122}{2*-1}=\frac{13122}{-2}
=-6561
$