I have a basic question about taking partial derivatives. Say I have a function of 3 variables and i want the derivative of only one. Do I take the derivative of the one variable and HOLD THE OTHER TWO CONSTANT? Or, do I take the derivative of the variable and TREAT THE OTHER TWO AS CONSTANTS? For example If I have f(x,y,z) = xy2+z3 and I want to find fx Does that mean I get 2xy or 2xy+z3? Like does that z drop out or do I literally not touch it? This isn't a homework question. I'm just trying to understand what the rule is.