Question

A ball is thrown into the air. The height h, in feet, of the ball can be modeled by the equation h= -16t^2+20t+6, where t is the time, in seconds, the ball is in the air. When will the ball hit the ground?

first should I use x= -b/2a?

Answer 1

-2(8t^2 -10t -6) = 0

-2(2t -3) (4t +1) = 0

2t -3 = 0

2t-3 + 3 = 0 + 3

2t = 3

t = 3/2 second

Answer 2

Solve the equation

-16t^2+20t+6 = 0
will give you the times that the ball is on the ground. The negative root accounts for the fact that the ball is 6 feet above ground at t=0.
I get t=3/2 and t=-1/4

Answer 3

x = -b/2a will give you the vertex. That will tell you how high the ball went if you plug it in and evaluate h.

Answer 4

Thank you to all

Answer 5

10 feet