How can I use Octave to answer these two questions?

We won’t do your homework for you. But we are happy to help if you have specific questions.

To answer these two questions, which part of the octave documentation (on disk or online) will be useful?

Google (or another search engine) is your friend. :wink:

meshgrid to generate the grid where the tails of the vectors reside (kind of; but not exactly).
arrayfun to evaluate the formula at each of these grid points. (sometime it can be done directly without arrayfun)
quiver to draw an arrow from the tail (grid point) to the head (output of the function).

type demo quiver and see what happens.