490=50t+4.9t^2

Solution for 490=50t+4.9t^2 equation:

490=50t+4.9t^2

We move all terms to the left:

490-(50t+4.9t^2)=0

We get rid of parentheses

-4.9t^2-50t+490=0

a = -4.9; b = -50; c = +490;
Δ = b2-4ac
Δ = -502-4·(-4.9)·490
Δ = 12104
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:

$\sqrt{\Delta}=\sqrt{12104}=\sqrt{4*3026}=\sqrt{4}*\sqrt{3026}=2\sqrt{3026}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-50)-2\sqrt{3026}}{2*-4.9}=\frac{50-2\sqrt{3026}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-50)+2\sqrt{3026}}{2*-4.9}=\frac{50+2\sqrt{3026}}{-9.8}
$