SOLUTION: A rocket shot into the aire has a height of s= 128t - 16t^2 feet, where t is the number of seconds after the rocket is shot. During what time after the rocket is shot is it atleas

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Question 728349: A rocket shot into the aire has a height of s= 128t - 16t^2 feet, where t is the number of seconds after the rocket is shot. During what time after the rocket is shot is it atleast 240 feet high??
Answer by nerdybill(7384) About Me  (Show Source):
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A rocket shot into the aire has a height of s= 128t - 16t^2 feet, where t is the number of seconds after the rocket is shot. During what time after the rocket is shot is it atleast 240 feet high??
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set s to 240 and solve for t:
s= 128t - 16t^2
240 = 128t - 16t^2
15 = 8t - t^2
t^2 + 15 = 8t
t^2 - 8t + 15 = 0
(t-3)(t-5) = 0
t = {3, 5}
answer: the entire time between 3 seconds and 5 seconds