[anujsharmax]

Be careful when using knowledge from this post. These are special cases, not the general rules of differentiaton (or calculus).

For example, for multi variable calculus, the results would be very different.

Let's take the example of W.X

d/dx (W.X) = X.d/dx(W) + W.d/dx(X)

since W is not dependent on x, the first term is zero and we get the answer the author got.

Before drawing conclusions from the post, please remember the assumptions the author has taken.