16=81x^2

Solution for 16=81x^2 equation:

16=81x^2

We move all terms to the left:

16-(81x^2)=0

a = -81; b = 0; c = +16;
Δ = b2-4ac
Δ = 02-4·(-81)·16
Δ = 5184
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5184}=72$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-72}{2*-81}=\frac{-72}{-162}
=4/9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+72}{2*-81}=\frac{72}{-162}
=-4/9
$