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Math Help - using f(t) = 3t/(t+3), what is the velocity of a train at t = 7

  1. #1
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    using f(t) = 3t/(t+3), what is the velocity of a train at t = 7

    For some reason, this is one of only two questions I'm stumped on right now.

    I've calculated the distance @ 21/10. But when I follow the examples in Stewart Calculus ed:7 I can't work out how to calculate the velocity.

    Time = 7, distance = 21/10. I'm not even close to the answer, or even sure how I'm supposed to go about the problem.

    Not asking for it to be done, just a step in the right direction.
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  2. #2
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    Re: using f(t) = 3t/(t+3), what is the velocity of a train at t = 7

    If f(t) is the distance function then f'(t) is the velocity function. Take the derivative and evaluate it when t = 7

    Please post your calculations so we can see where you need help.

    Thanks from MarkFL and limitofx
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    Re: using f(t) = 3t/(t+3), what is the velocity of a train at t = 7

    cheers, I missed the concept for this one early on and was off on a tangent.

    Sometimes these are so easy once you know what to do.

    I basically did [g(f')- f(g')] / g^2 plugging in values and it was straight forward.

    ended up with 9/100.
    Thanks from agentmulder
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