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Homework Help: Implicit diff

  1. Mar 2, 2013 #1
    1. The problem statement, all variables and given/known data

    2y = cot(x-y)

    3. The attempt at a solution

    2y' = -csc2 (x-y) . (1-y)(y')

    Is it correct so far?

    My book actually has

    2y' = -csc^2 (x-y) + y' csc^2(x-y)

    And I don't understand where that sum comes from. Am I supposed to apply the product rule? Because I tried and it didn't get me to that step the book presents.
    Last edited: Mar 2, 2013
  2. jcsd
  3. Mar 2, 2013 #2


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    Homework Helper

    Your mistake would be in differentiating (x-y) wrt to x.

    d/dx(x-y) = 1 - d/dx(y)
  4. Mar 2, 2013 #3
    Thanks for the reply :)

    But where does the sum sign come from?

    Because even if it's 1 - y'

    I will be still multiplying, as below:

    -csc2 (x-y) . (1- y')
  5. Mar 2, 2013 #4


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    Science Advisor
    Homework Helper

    Multiply it out. Use that a(b+c)=ab+ac.
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