Algebra
posted by Casey on .
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?

2(8t^2 10t 6) = 0
2(2t 3) (4t +1) = 0
2t 3 = 0
2t3 + 3 = 0 + 3
2t = 3
t = 3/2 second 
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 
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.

Thank you to all