Greeting A TA has got me very and utterly confused. He won't be avaible for a few days, so I'm asking you guys. Consider the transformation to cilindrical coord. x-->r.con[the] y-->r.sin[the] z-->z I have the Jabobian (no problems here). He then asks the differential da , where a is a vector. Enter the first confusion. I know the differential of the transformation (the linear function given by the Jacobian matrix), but what the hell is the differential of a vector? My guess is: da =dxx +dyy +dzz . I have the unity vectors of the new system. The trick is now what is dr in fuction of the new unity vectors? Then answer : da =drr +rd[the][the] +dzz How the hell is this determined?