lain throws ball....

Question

Lain throws a ball into the air. Its height above ground after x seconds is 2+4x-4.9x²  meters. How long does it take for the ball to hit the ground? 

Answer 1

For for x in

 

-4.9x² + 4x + 2 = 0

 

You can use the quadratic formula.  One solution will be negative, the other positive.  Keep only the positive solution, since time starts at zero.