Posted by **Casey** on Thursday, June 6, 2013 at 4:07pm.

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?

- Algebra -
**Kuai**, Thursday, June 6, 2013 at 4:17pm
-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

- Algebra -
**MathMate**, Thursday, June 6, 2013 at 4:19pm
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

- Algebra -
**Steve**, Thursday, June 6, 2013 at 4:25pm
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.

- Algebra -
**Casey**, Thursday, June 6, 2013 at 5:47pm
Thank you to all

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