85=4.9t^2

Solution for 85=4.9t^2 equation:

85=4.9t^2

We move all terms to the left:

85-(4.9t^2)=0

We get rid of parentheses

-4.9t^2+85=0

a = -4.9; b = 0; c = +85;
Δ = b2-4ac
Δ = 02-4·(-4.9)·85
Δ = 1666
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:

$\sqrt{\Delta}=\sqrt{1666}=\sqrt{1*1666}=\sqrt{1}*\sqrt{1666}=1\sqrt{1666}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-1\sqrt{1666}}{2*-4.9}=\frac{0-1\sqrt{1666}}{-9.8}
=-\frac{1\sqrt{1666}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+1\sqrt{1666}}{2*-4.9}=\frac{0+1\sqrt{1666}}{-9.8}
=\frac{1\sqrt{1666}}{-9.8}
$