Hi, So, I am reviewing Cal III, and I have come across something that I do not understand regarding implicit differentiation with partial derivatives: x^3 + y^3 + z^3 + 6xyz = 1 implicit differentiation of z with respect to x: 3x^2 + 3z^2(dz/dx) + 6yz + 6xy(dz/dx) = 0 *notive the (dz/dx) are partial derivatives, not regular derivatives What I do not understand is that there are two '6xyz' derivatives. I understand how 6yz was formed, because it is wrt x, and the 6xy(dz/dx) because that is how the implicit part works, I believe. However, I do not understand how you can just add the variables twice, it seems like that would change this entire equality. . . ? Any help would be great! Thanks!