0=-4.9t^2-8t+400

Solution for 0=-4.9t^2-8t+400 equation:

0=-4.9t^2-8t+400

We move all terms to the left:

0-(-4.9t^2-8t+400)=0

We add all the numbers together, and all the variables

-(-4.9t^2-8t+400)=0

We get rid of parentheses

4.9t^2+8t-400=0

a = 4.9; b = 8; c = -400;
Δ = b2-4ac
Δ = 82-4·4.9·(-400)
Δ = 7904
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:

$\sqrt{\Delta}=\sqrt{7904}=\sqrt{16*494}=\sqrt{16}*\sqrt{494}=4\sqrt{494}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-4\sqrt{494}}{2*4.9}=\frac{-8-4\sqrt{494}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+4\sqrt{494}}{2*4.9}=\frac{-8+4\sqrt{494}}{9.8}
$