0=-4.9t2+4.25t+100

Solution for 0=-4.9t2+4.25t+100 equation:

0=-4.9t^2+4.25t+100

We move all terms to the left:

0-(-4.9t^2+4.25t+100)=0

We add all the numbers together, and all the variables

-(-4.9t^2+4.25t+100)=0

We get rid of parentheses

4.9t^2-4.25t-100=0

a = 4.9; b = -4.25; c = -100;
Δ = b2-4ac
Δ = -4.252-4·4.9·(-100)
Δ = 1978.0625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4.25)-\sqrt{1978.0625}}{2*4.9}=\frac{4.25-\sqrt{1978.0625}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4.25)+\sqrt{1978.0625}}{2*4.9}=\frac{4.25+\sqrt{1978.0625}}{9.8}
$