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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.

 Jul 18, 2020
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Just put in 77 for y ...then solve for 't ' using the Quadratic formula

 

77 = - 6t2 + 43t   

-6t2 +43t -77 = 0 

 

    a = -6     b = 43    c = -77

 

\(t = {-b \pm \sqrt{b^2-4ac} \over 2a}\)          throw out any negative 't' values

 Jul 18, 2020
edited by ElectricPavlov  Jul 18, 2020

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