81.25=x^2

Solution for 81.25=x^2 equation:

81.25=x^2

We move all terms to the left:

81.25-(x^2)=0

We add all the numbers together, and all the variables

-1x^2+81.25=0

a = -1; b = 0; c = +81.25;
Δ = b2-4ac
Δ = 02-4·(-1)·81.25
Δ = 325
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{325}=\sqrt{25*13}=\sqrt{25}*\sqrt{13}=5\sqrt{13}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-5\sqrt{13}}{2*-1}=\frac{0-5\sqrt{13}}{-2}
=-\frac{5\sqrt{13}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+5\sqrt{13}}{2*-1}=\frac{0+5\sqrt{13}}{-2}
=\frac{5\sqrt{13}}{-2}
$