0=100-2x-4.9x^2

Solution for 0=100-2x-4.9x^2 equation:

0=100-2x-4.9x^2

We move all terms to the left:

0-(100-2x-4.9x^2)=0

We add all the numbers together, and all the variables

-(100-2x-4.9x^2)=0

We get rid of parentheses

4.9x^2+2x-100=0

a = 4.9; b = 2; c = -100;
Δ = b2-4ac
Δ = 22-4·4.9·(-100)
Δ = 1964
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:

$\sqrt{\Delta}=\sqrt{1964}=\sqrt{4*491}=\sqrt{4}*\sqrt{491}=2\sqrt{491}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{491}}{2*4.9}=\frac{-2-2\sqrt{491}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{491}}{2*4.9}=\frac{-2+2\sqrt{491}}{9.8}
$