170=9.8t^2

Solution for 170=9.8t^2 equation:

170=9.8t^2

We move all terms to the left:

170-(9.8t^2)=0

We get rid of parentheses

-9.8t^2+170=0

a = -9.8; b = 0; c = +170;
Δ = b2-4ac
Δ = 02-4·(-9.8)·170
Δ = 6664
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:

$\sqrt{\Delta}=\sqrt{6664}=\sqrt{4*1666}=\sqrt{4}*\sqrt{1666}=2\sqrt{1666}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{1666}}{2*-9.8}=\frac{0-2\sqrt{1666}}{-19.6}
=-\frac{2\sqrt{1666}}{-19.6}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{1666}}{2*-9.8}=\frac{0+2\sqrt{1666}}{-19.6}
=\frac{2\sqrt{1666}}{-19.6}
$