Question 967064
Ricardo throws a stone off a bridge into a river below. The stone's height above the water in meters, y, is dependent on time in seconds after throwing, x, and can be modeled with the function 
y=−5(x−8)(x+4)
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y = -5(x^2 -4x -32) = -5x^2 + 20x + 160
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 How many seconds after being thrown will the stone hit the water? seconds
Solve -5(x-8)(x+4) = 0
Ans: x = 8 seconds
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What is the maximum height that the stone will reach? meters
Vertex occurs at x = -b/(2a) = -20/(-10) = 2 seconds
Max height = f(2) = -5(-6)(6) = 180 meters
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How many seconds after being thrown will the stone reach its maximum height? seconds
Ans: 2 seconds (from vertex work above)
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What is the height of the stone at the time it is thrown? 
Ans: f(0) = 160 meters
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Cheers,
Stan H.
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