0=9t-4.9t^2

Solution for 0=9t-4.9t^2 equation:

0=9t-4.9t^2

We move all terms to the left:

0-(9t-4.9t^2)=0

We add all the numbers together, and all the variables

-(9t-4.9t^2)=0

We get rid of parentheses

4.9t^2-9t=0

a = 4.9; b = -9; c = 0;
Δ = b2-4ac
Δ = -92-4·4.9·0
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-9}{2*4.9}=\frac{0}{9.8}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+9}{2*4.9}=\frac{18}{9.8}
=1+6.8333333333333/8.1666666666667
$