1. The problem statement, all variables and given/known data there is a question and a solution in this page; http://www.fen.bilkent.edu.tr/~otekman/math102/s03/m2q5.html Please firstly examine the question and solution. (5b)... There it says f(x,y)=z and x=g(r,teta) and y=h(r,teta) and asks fxx. He solves this problem by starting so; fx=zr*rx+zteta*tetax ... My question is that by writing fx such as above aren't you assume that r and teta are a function of x? However in the question it says x=f(r,teta); this means x is a function of r and teta then how can you write fx=zr*rx+zteta*tetax? Isn't there a contradiction or am i understanding something false?