Greetings ! I'd appriciate some help in explaining, in general, what - extracting partial differentials of a function, means. I'm talking about a function like f(x,y,z). Does it mean that I need a single solution where I will have differentials for x,y,z of the func.? Example: f'(x,y,z) = ( x^2*y + y^2*z + x*e^(2z) )' = = (2x*y + e^(2z))x' + (x^2 + 2y*z)y' + (y^2 + 2e^(2z))z' Also (this is related to physics), if I have unit vectors of x, y, z in the func. do they stay as they were or does it entail doing some tricks on them as well (for Cartesian coordinates - I don't think I should touch'em, but what about a func. of polar coordinates - discribing the course of the particle itself). Thanks ! Live long and prosper.