4.905t^2-6.9t+0.65=0

Solution for 4.905t^2-6.9t+0.65=0 equation:

4.905t^2-6.9t+0.65=0

a = 4.905; b = -6.9; c = +0.65;
Δ = b2-4ac
Δ = -6.92-4·4.905·0.65
Δ = 34.857
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{-(-6.9)-\sqrt{34.857}}{2*4.905}=\frac{6.9-\sqrt{34.857}}{9.81}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6.9)+\sqrt{34.857}}{2*4.905}=\frac{6.9+\sqrt{34.857}}{9.81}
$