Dear Vadique,

thank you for the question!

I fixed your mistake and gave you right formula. Please see attached file.

Thanks for answering, Tatiana

For first part I got that, having p × q = –( q × p ) for any two vectors p & q, and that derivation of vector by coordinate (which is scalar) gives a vector too, so when I swap multipliers *before* applying the nabla, then minus sign appears.

For second part, I don’t understand down arrow above notation. Is it how the product rule d(pq) = (dp)q + p(dq) applies here?

Dear Vadique,

the operator nabla is differential, so we use the rules of differential algebra, and you are right. When you derive formulas, use the operator’s representation in the form: nabla=e_i (d/dx_i) that will be easier for you.

Thank you again. Now I wrote it this way (attached picture)

You're absolutely right!

using index notation