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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.

 Mar 19, 2020
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y = -16t^2 +80 t         describes the height.....soooooo

height = 36 ft

36 = -16 t^2 +80t    

-16t^2+80t -36 =0       Now use the Quadratic Formula to determine the values of t.....there will be TWO....one (the smaller) will be on the way up and the other will be t for the way down.....obviously you want the smaller one....

 

  \(t = {-b \pm \sqrt{b^2-4ac} \over 2a}\)    a = -16    b = 80    c = -36         You should be able to do this now....or you are in the wrong class for your abilities so far

 Mar 19, 2020

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