-4.9*x^2+20.8*x+3=0

Solution for -4.9*x^2+20.8*x+3=0 equation:

-4.9x^2+20.8x+3=0

a = -4.9; b = 20.8; c = +3;
Δ = b2-4ac
Δ = 20.82-4·(-4.9)·3
Δ = 491.44
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20.8)-\sqrt{491.44}}{2*-4.9}=\frac{-20.8-\sqrt{491.44}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20.8)+\sqrt{491.44}}{2*-4.9}=\frac{-20.8+\sqrt{491.44}}{-9.8}
$