Prob.1 (15) The level curves of a function $f$ are shown on the right.
(a) What is (roughly) the direction of $
abla f$ at (1, 6).
(b) Is $f_x(4, 6)$ is positive or negative. Explain why so.
(c) Which is greater, $f_y(6, 2)$ or $f_y(6, 5)$? Explain why so.