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modphysnoob
@JamesJ,@TuringTest can you explain me this
What part do you not understand?
\[x=r\cos\theta\]\[y=r\sin\theta\]\[z=z\]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.
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