Thread: Variable substitution in a derivative

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I can't derivate about dx anymore, as I don't have the variable x, it has been replaced by x=r*cos(theta) and y=r*sin(theta)...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

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

download the pdf file that is attached in the first post.

3. Thanks for the info on Latex, anybody has an idea for the first question?