200=9.8t^2

Solution for 200=9.8t^2 equation:

200=9.8t^2

We move all terms to the left:

200-(9.8t^2)=0

We get rid of parentheses

-9.8t^2+200=0

a = -9.8; b = 0; c = +200;
Δ = b2-4ac
Δ = 02-4·(-9.8)·200
Δ = 7840
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:

$\sqrt{\Delta}=\sqrt{7840}=\sqrt{16*490}=\sqrt{16}*\sqrt{490}=4\sqrt{490}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{490}}{2*-9.8}=\frac{0-4\sqrt{490}}{-19.6}
=-\frac{4\sqrt{490}}{-19.6}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{490}}{2*-9.8}=\frac{0+4\sqrt{490}}{-19.6}
=\frac{4\sqrt{490}}{-19.6}
$