## anonymous 3 years ago @JamesJ,@TuringTest can you explain me this

1. anonymous

2. TuringTest

What part do you not understand?

3. anonymous

I meant ds

4. TuringTest

$x=r\cos\theta$$y=r\sin\theta$$z=z$Then you need the Jacobian of the transformation... or you can just memorize that when switching to cylindrical or polar coordinates you pick up an extra r in the differential.

5. TuringTest

check out example 2: http://tutorial.math.lamar.edu/Classes/CalcIII/ChangeOfVariables.aspx try the same trick for cylindrical coordinates and you will find that you get the same thing i.e. the extra r