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Need calc help 1 last time.

  1. Jul 15, 2005 #1
    hi there i am having trouble on the following question.

    1. ln(x+y) = e^3x
    (1/x+y)(1+(dy/dx)) = (e^3x)(3)
    what can u substititue for y???
    Last edited: Jul 15, 2005
  2. jcsd
  3. Jul 15, 2005 #2


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    Homework Helper

    I take it you are finding dy/dx by implict differentiation?
    differentiation yeilds
    solving for dy/dx
    observe x+y=exp(exp(3x))
    observe that one could solve the original equation for y and obtain a more straitforward solution.
    solve for y
  4. Jul 15, 2005 #3
    You're not meant to do people's work for them :/.
  5. Jul 15, 2005 #4
    how do u get e^e^3x
  6. Jul 15, 2005 #5
    By solving the natural log.
  7. Jul 15, 2005 #6
    ok thanks guys.
  8. Jul 15, 2005 #7


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    Staff Emeritus
    Science Advisor

    In general, however, when doing an implicit differentiation, it is not necessary nor desirable to solve for y and then substitute that for y in the expression for the derivative. It is better to leave it in terms of both x and y.
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