4.9*x^2-7.07*x-20=0

Solution for 4.9*x^2-7.07*x-20=0 equation:

4.9x^2-7.07x-20=0

a = 4.9; b = -7.07; c = -20;
Δ = b2-4ac
Δ = -7.072-4·4.9·(-20)
Δ = 441.9849
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{-(-7.07)-\sqrt{441.9849}}{2*4.9}=\frac{7.07-\sqrt{441.9849}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7.07)+\sqrt{441.9849}}{2*4.9}=\frac{7.07+\sqrt{441.9849}}{9.8}
$