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Please explain to work this:

A rocket is launched from atop a 105-foot cliff with an initial velocity of 156ft/s. the height of the rocket above the ground at time t is given by

h= -16t^2 + 156t + 105. When will the

rocket hit the ground after it is launched? Round to the nearest second.

  • math -

    naturally, when h = 0.

    -16t^2 + 156t + 105 = 0
    t = (39 ± √1941)/8
    t = 10 sec

  • math -

    ???????????????????????????????????????Your confusing me! STOP CONFUSING ME!!!!!

  • math -

    h=0, so you set this up in the quadratic formula, which then you follow all the rules and your left with a positive and negative answer. time cant be negative, so the correct answer should be about 10.38 seconds which rounds off to 10.4

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