问题标题：
QuadraticFunctionsWordProblem数学,函数,方程Aballisthrownupintotheair.Itsheighth,inmetres,aftertsecondsish=-4.9t^2+38t+1.75.Forwhatlengthoftimeistheballabove50m?希望解答.希望写出过程.谢谢.
问题描述：
QuadraticFunctionsWordProblem数学,函数,方程
Aballisthrownupintotheair.Itsheighth,inmetres,aftertsecondsish=-4.9t^2+38t+1.75.Forwhatlengthoftimeistheballabove50m?
希望解答.希望写出过程.谢谢.
石彤菊回答：
Solution:
Lethbe50m
-4.9t²+38t+1.75=50
4.9t²-38t+48.25=0
t₁=1.60s
t₂=6.16s
TimedurationΔt=6.16-1.60=4.56(s)
Ans:Thelengthoftimeis4.56seconds.
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