The ball is throw in to the air . If its height in feet is given by - 16t^2 + 64t, at what time t will the ball reach a height of 64 feet?
just solve
- 16t^2 + 64t = 64
Let's get rid of that pesky factor of -16, leaving
t^2 - 4t + 4 = 0
(t-2)^2 = 0
t = 2