There's a vector field,

**A**(

**r**) = x(

**x-hat**) + y(

**y-hat**) + z^2(

**z-hat**) and my notes say:

"Note that

**rho-hat**= cos phi(

**x-hat**) + sin phi(

**y-hat**) and

**phi-hat**= -sin phi(

**x-hat**) + cos phi(

**y-hat**) and so

**A**(

**r**) = rho(

**rho-hat**) + z^2(

**z-hat**)".

Why?? I can't see any obvious connection between phi-hat, rho-hat and x and y .