2+21.5t-4.9t^2=0

Solution for 2+21.5t-4.9t^2=0 equation:

2+21.5t-4.9t^2=0

a = -4.9; b = 21.5; c = +2;
Δ = b2-4ac
Δ = 21.52-4·(-4.9)·2
Δ = 501.45
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21.5)-\sqrt{501.45}}{2*-4.9}=\frac{-21.5-\sqrt{501.45}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21.5)+\sqrt{501.45}}{2*-4.9}=\frac{-21.5+\sqrt{501.45}}{-9.8}
$