Good afternoon guys! I have some doubts about partial derivatives. The other day, my analytic geometry professor told us that slopes do not exist in three-dimensional space. If that's the case, then what does a partial derivative represent? Given that the derivative of a function with respect to one variable is the slope of the tangent line to some point of that function. Also, if a partial derivative is the rate of change of just one variable in a function of several variables, is there a way to calculate the total rate of change of the function? Thanks in advance!