Is it true that (dy/dx) = 1/(dx/dy) ? Is it still true if these are partial derivatives of a function of multiple variables? (All this, assuming that the inverse function exists) Can anybody prove it in terms of the definition of a derivative? or any sort elementary proof at all? (I can almost convince my self it is true with Linear Algebra). I haven't seen it proven in any books, but it is true for all of the functions I know of. Can I get a definitive answer?