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The equation $y = -16t^2 + 80t$ describes the height (in feet) of a projectile launched from the ground at 80 feet per second. At what $t$ will the projectile reach 36 feet in height for the first time? Express your answer as a decimal rounded to the nearest tenth.

 Jul 23, 2022
 #1
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-16t^2 + 80t =  36

 

-16t^2 + 80t  - 36 =  0          divide through by -4

 

4t^2  -20t + 9  = 0

 

(2t -1) (2t - 9)  = 0

 

The first factor set =  0  is what we need

 

2t -  1 =  0

 

2t =1

 

t =  1/2 sec =  .5 sec

 

 

cool cool cool

 Jul 23, 2022
edited by CPhill  Jul 23, 2022

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