50=0.81t^2

Solution for 50=0.81t^2 equation:

50=0.81t^2

We move all terms to the left:

50-(0.81t^2)=0

We get rid of parentheses

-0.81t^2+50=0

a = -0.81; b = 0; c = +50;
Δ = b2-4ac
Δ = 02-4·(-0.81)·50
Δ = 162
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{162}=\sqrt{81*2}=\sqrt{81}*\sqrt{2}=9\sqrt{2}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-9\sqrt{2}}{2*-0.81}=\frac{0-9\sqrt{2}}{-1.62}
=-\frac{9\sqrt{2}}{-1.62}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+9\sqrt{2}}{2*-0.81}=\frac{0+9\sqrt{2}}{-1.62}
=\frac{9\sqrt{2}}{-1.62}
$