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Rate of change of area of circle in respect to radius

  1. Feb 25, 2014 #1
    What is the Rate of change of area of circle in respect to radius when radius is 3in
    I know that that dA/dr is equal to the circumference of the circle
    But where does that come from?
    Also the formula for the circumference of the circle is 2(pi)r
    But the answer is 6 (pi)in^2/in.
    I understand the 6 but where are the units coming from if the circumference of the circle will only give you units for r ?

    Hope someone can shed some light on this for me! Thanks
     
  2. jcsd
  3. Feb 25, 2014 #2

    PhysicoRaj

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    It is rate of change of AREA wrt RADIUS. What are the units of these two?
     
  4. Feb 25, 2014 #3

    Ok so you basically use the formula for the circumference of the circle but use the units for area/radius?
     
  5. Feb 25, 2014 #4

    PhysicoRaj

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    Both are one and the same. But since we are representing the rate of change, it is better to use units like that.
     
  6. Feb 25, 2014 #5

    Thank you.
     
  7. Feb 25, 2014 #6

    Integral

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    Homework questions need to be posted in the homework forums.
     
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