0=20-4.9x^2

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

0=20-4.9x^2

We move all terms to the left:

0-(20-4.9x^2)=0

We add all the numbers together, and all the variables

-(20-4.9x^2)=0

We get rid of parentheses

4.9x^2-20=0

a = 4.9; b = 0; c = -20;
Δ = b2-4ac
Δ = 02-4·4.9·(-20)
Δ = 392
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{392}=\sqrt{196*2}=\sqrt{196}*\sqrt{2}=14\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14\sqrt{2}}{2*4.9}=\frac{0-14\sqrt{2}}{9.8}
=-\frac{14\sqrt{2}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14\sqrt{2}}{2*4.9}=\frac{0+14\sqrt{2}}{9.8}
=\frac{14\sqrt{2}}{9.8}
$