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The equation $y = -6t^2 + 43t$ describes the height (in feet) of a projectile $t$ seconds after it is launched from the surface of Mars at 43 feet per second. In how many seconds will the projectile first reach 77 feet in height? Express your answer as a decimal rounded to the nearest tenth.

 Apr 24, 2020
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y  =  -6·t2 + 43·t

 

If  y = 77:     77  =   -6·t2 + 43·t     --->     6·t2 - 43·t + 77  =  0

 

Using the quadratic formula:  t is either  44/12  or  42/12.

 

Choosing the first answer to occur:  42/12  =  ...

 Apr 24, 2020

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