25=81x2

Solution for 25=81x2 equation:

25=81x^2

We move all terms to the left:

25-(81x^2)=0

a = -81; b = 0; c = +25;
Δ = b2-4ac
Δ = 02-4·(-81)·25
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-90}{2*-81}=\frac{-90}{-162}
=5/9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+90}{2*-81}=\frac{90}{-162}
=-5/9
$