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Homework Help: Related Rates

  1. Apr 24, 2005 #1
    Hi Again,

    I am doing a question on related rates that I have become stuck on.

    The height (h) of an equilateral triangle is increasing at a rate of 3cm/min. How fast is the area changing when h is 5cm?

    I know that the area of a triangle is bh/2, but after that I am stuck :redface: I tried deriving it using the chain rule so that I could substitute h and the rate of h, but I don't think that i was doing it the right way. If anyone could direct me here I would really appreciate the help.
  2. jcsd
  3. Apr 24, 2005 #2
    Here are some things to consider, the height "h" of an equilateral triangle is


    where "s" is the length of one side.

    The area of this triangle is equal to


    See any substitutions?
  4. Apr 24, 2005 #3
    \frac{dA}{dt} = \frac{dh}{dt} * \frac{dA}{dh}
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