0=4.9t^2+4t-100

Solution for 0=4.9t^2+4t-100 equation:

0=4.9t^2+4t-100

We move all terms to the left:

0-(4.9t^2+4t-100)=0

We add all the numbers together, and all the variables

-(4.9t^2+4t-100)=0

We get rid of parentheses

-4.9t^2-4t+100=0

a = -4.9; b = -4; c = +100;
Δ = b2-4ac
Δ = -42-4·(-4.9)·100
Δ = 1976
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1976}=\sqrt{4*494}=\sqrt{4}*\sqrt{494}=2\sqrt{494}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{494}}{2*-4.9}=\frac{4-2\sqrt{494}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{494}}{2*-4.9}=\frac{4+2\sqrt{494}}{-9.8}
$