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The equation y = -6t^2 + 51t describes the height (in feet) of a projectile launched from the surface of Mars at 51 feet per second. In how many seconds will the projectile first reach 108 feet in height?

 Aug 9, 2020
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y  =  -6t2 + 51t

y = 108

 

Combining:                        -6t2 + 51t  =  108

                                 -6t2 + 51t - 108  =  0

Multiplying by -1:      6t2 -  51t + 108  =  0

Dividing by 3:              2t2 - 17t + 36  =  0

Factoring:                      (2t - 9)(t - 4)  =  0

 

Answer:  Either  t = 4.5  or  t = 4

 Aug 9, 2020

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