are continuous. 12. The function 2 +21 f(z, y) = (x, 1/) + (0, 0) (x, y) = (0,0) at the point (To, yo) = (0, 0). 13. The function g(r, y) = [ryl at (0, 0). 14. The function q(r, y) = z + 3y - 1 at (0, 1). 15 (no submission). Plot the functions from #11-#14 in CalcPlot3D, as well as their first-order ap mations. Convince yourself that when a function is differentiable, the first-order approximation is ind good approximation everywhere near the given point, and when it's not a good approximation, the fur is not differentiable. 16. Theorem 2 in the notes asserts that if f is continuous at a given point, and all of its partials ar continuous functions at the given point, then f is differentiable. Which of the following functions can you immediately say are differentiable, using Theorem 2, wit doing any limit computations? You do not need to justify your answer. a) The function at the point (0, 0). b) The function In(r + y) at the point (2, -1). c) The function Vx2 + 92 at the point (0, 0). d) The function 247 7 at the point (0, 0)