100=4.9x^2

Solution for 100=4.9x^2 equation:

100=4.9x^2

We move all terms to the left:

100-(4.9x^2)=0

We get rid of parentheses

-4.9x^2+100=0

a = -4.9; b = 0; c = +100;
Δ = b2-4ac
Δ = 02-4·(-4.9)·100
Δ = 1960
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:

$\sqrt{\Delta}=\sqrt{1960}=\sqrt{4*490}=\sqrt{4}*\sqrt{490}=2\sqrt{490}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{490}}{2*-4.9}=\frac{0-2\sqrt{490}}{-9.8}
=-\frac{2\sqrt{490}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{490}}{2*-4.9}=\frac{0+2\sqrt{490}}{-9.8}
=\frac{2\sqrt{490}}{-9.8}
$