100=-4.9x^2+102x+100

Solution for 100=-4.9x^2+102x+100 equation:

100=-4.9x^2+102x+100

We move all terms to the left:

100-(-4.9x^2+102x+100)=0

We get rid of parentheses

4.9x^2-102x-100+100=0

We add all the numbers together, and all the variables

4.9x^2-102x=0

a = 4.9; b = -102; c = 0;
Δ = b2-4ac
Δ = -1022-4·4.9·0
Δ = 10404
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{10404}=102$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-102)-102}{2*4.9}=\frac{0}{9.8}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-102)+102}{2*4.9}=\frac{204}{9.8}
=20+8/9.8
$