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The equation y = -16t^2 - 60t + 54 describes the height (in feet) of a ball thrown downward at 60 feet per second from a height of 54 feet from the ground, where t represents time, measured in seconds. In how many seconds will the ball reach a height of 20 feet? Express your answer as a decimal rounded to the nearest hundredth. 

 Jul 13, 2022

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 #1
avatar+128448 
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-16t^2  -60t  + 54 = 20

 

-16t^2 -60t + 34  = 0

 

16t^2  + 60t  - 34  =  0

 

 

              -60   +  sqrt [ 60^2  - 4 (16) (-34) ]               -60 + sqrt [ 5776]       

t  =       _____________________________   =     ________________ =

                              2 * 16                                                   32

 

 

-60 + 76

_______  =   16 / 32  =     .5 sec

      32

 

 

cool cool cool

 Jul 13, 2022

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