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Homework Help: Implicit functions

  1. Nov 3, 2008 #1


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    1. The problem statement, all variables and given/known data

    Find dy/dx of y^2+2y = x^3+3x-1

    2. Relevant equations

    3. The attempt at a solution

    I devided both sides by y so i got y+2 = x^3+3x-1/y
    then differentiating i got dy/dx = 3x^2 +3 / dy/dx

    I don't think this is right
    thanks for any help
  2. jcsd
  3. Nov 3, 2008 #2


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    What you should have gotten was

    dy/dx = 3x2 + 3 + 1/y2*dy/dx

    As when you differentiate 1/y with respect to x, by the chain rule you get 1/y2*dy/dx To avoid y's in the denominator, it's probably better to start by differentiating rather than dividing both sides by y (you also put off corner cases where y=0 to be dealt with later.... and procrastination is always good)
  4. Nov 3, 2008 #3


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