Question

A ball is thrown straight up from a bridge over a river and falls into the water. The height, h, in meters, of the ball above the water t seconds after being thrown is approximately modeled by the relation h=-5t^2+10t+35.

c) After how many seconds does the ball hit the water?

Answer 1

since h is the height above the water, it hits the water when h=0:

-5t^2+10t+35 = 0
t = 1+2√2

Answer 2

Where did you get the 1 + 2 square root 2 for the answer? Please explain more thoroughly for the answer and how you got it.