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Homework Help: Related rates of change

  1. Oct 16, 2013 #1
    1. The problem statement, all variables and given/known data
    A street light is at the top of a pole that is 18 feet tall. A woman 6 ft tall walks away from the pole with a speed of 4 ft/sec along a straight path. How fast is the length of her shadow moving when she is 35 ft from the base of the pole?

    2. Relevant equations

    a^2 + b^2 = c^2
    b' = 4

    3. The attempt at a solution

    18/6 relate to

    I got x = 35/2

    so total length of side is 105/2

    18^2 + 105/2 ^ 2 = 111/2 ^ 2

    2aa' + 2bb' = 2cc'

    a' = 0, height of pole never changes

    2*35*4 = 111/2 * c'

    c' = 420/111

    but wrong anwser
    Last edited: Oct 16, 2013
  2. jcsd
  3. Oct 16, 2013 #2


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    Science Advisor
    Homework Helper

    You should at least explain what your variables mean. Could you do that?
  4. Oct 17, 2013 #3
    Are you looking for the rate at which the shadow is moving relative to the person or relative to the base of the light pole ?
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