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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

    [tex]\frac{1}{2}\sqrt{3}s[/tex]

    where "s" is the length of one side.

    The area of this triangle is equal to

    [tex]\frac{1}{2}sh[/tex]

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