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Math Help - Variable substitution in a derivative

  1. #1
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    Variable substitution in a derivative

    f'(z) = du(x,y)/dx + i dv(x,y)/dx with z=x+iy

    Hi,

    What happens when I change for z=r*(cos(theta) + i*sin(theta))?

    I get:

    f'(z) = du(r*cos(theta),r*sin(theta))/dx + i dv(r*cos(theta),r*sin(theta))/dx

    I can't derivate about dx anymore, as I don't have the variable x, it has been replaced by x=r*cos(theta) and y=r*sin(theta)... What happens to the derivative?

    Btw, how to use the MATH tags??? I looked in the wiki and FAQ but found nothing...

    Thanks!
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  2. #2
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    http://www.mathhelpforum.com/math-he...-tutorial.html

    download the pdf file that is attached in the first post.
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  3. #3
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    Thanks for the info on Latex, anybody has an idea for the first question?
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