Hello everyone... I'm very confused.... i'm suppose to find dz/dt and dw/dt but for some of the questions there is no w variable! so what do u put for dw/dt?! Also i have the following: w = xy + yz^2; x = e^t; y = e^t*sint; z = e^t*cost; so i'm trying to find dz/dt and dw/dt; dz/dt = dz/dx * dx/dt + dz/dy * dy/dt + dz/dw * dw/dt; but when i try dz/dx * dx/dt i need to first take the partial derivative of z with respect to x, but as you can see, z has no x variable!! so what do i do about that? THanks!