Question 169698
a ball is thrown up into the air. its height h, in meters, after t seconds is 
h=-4.9t^2+38t+1.75.
for what length of time is the ball above 50 m?
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{{{graph(400,300,-10,20,-10,120,-4.9x^2 + 38x + 1.75,50)}}}
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-4.9x^2 + 38x + 1.75 = 50
-4.9x^2 + 38x - 48.25 = 0
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x = [-38 +- sqrt(38^2 - 4*-4.9*-48.25)]/-9.8
x = 1.59973..; x = 6.1554
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Total time at or above 50 m: 6.1554-1.59973 = 4.55564.. seconds
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Cheers,
Stan H.