Hello everyone.
My question is about deriving the Del (gradient) operator of cylindrical coordinates. I have reached the step of the theta term of the formula. where d/dtheta term is multiplied bu 1/r -or equivalently 1/rho- The question is attached .

Waiting your clarification.

 

Write your unit vectors in one coordinate system in terms of the unit vectors in the other. Then crank through the math.

 

I got it. It comes from the derivative of arctan(y/x) with respect to x

 

That one is for cylindrical coordinates