0=-4.9t^2-9t+900

Solution for 0=-4.9t^2-9t+900 equation:

0=-4.9t^2-9t+900

We move all terms to the left:

0-(-4.9t^2-9t+900)=0

We add all the numbers together, and all the variables

-(-4.9t^2-9t+900)=0

We get rid of parentheses

4.9t^2+9t-900=0

a = 4.9; b = 9; c = -900;
Δ = b2-4ac
Δ = 92-4·4.9·(-900)
Δ = 17721
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:

$\sqrt{\Delta}=\sqrt{17721}=\sqrt{9*1969}=\sqrt{9}*\sqrt{1969}=3\sqrt{1969}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-3\sqrt{1969}}{2*4.9}=\frac{-9-3\sqrt{1969}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+3\sqrt{1969}}{2*4.9}=\frac{-9+3\sqrt{1969}}{9.8}
$