z = f(x, y) = x - y-18-z-y+81. At time t=1, the particle has a position equal to (5,3, f(5,3)). The speed in x direction is axat-2 and speed in y direction equal to dyat=3. What is the velocity dzat of the particle in the z direction at this time? A function z=g(x,y) has partial derivatives zx-8-x and azdy=1. we rewrite the function of cylindrical coordinates, i.e. z-g(r,0). What then are partial derivatives in relation to 9 and r? 90 gr = || ||