Question 215011
solve 42 = -21t + 4.9t^2
4.9t^2 - 21t - 42 = 0
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Use the Quadratic Formula:
t = [21 +- sqrt(21^2 - 4*4.9*-42)]/9.8
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t = [21 +- sqrt(1264)]/9.8
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t = [21 +- 35.56]/9.8
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t = [21+35.56]/9.8 or t = [21-35.56]/9.8
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t = 0.5771... or -1.486..
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Cheers,
Stan H.