1.17. Let f : R2 -> R be the function: f (x, y) = Vat+ yt. (a) Find formulas for the partial derivatives or a of and ay 1 of at all points (x, y) other than the origin. (b) Find the values of the partial derivatives ox ( of (0, 0) and 24(0, 0). (Note that the formulas you found in part (a) probably do not apply at (0, 0).) 110 CHAPTER 4. REAL-VALUED FUNCTIONS: DIFFERENTIATION (c) Use the definition of differentiability to determine whether f is differentiable at (0, 0). (Hint: Polar coordinates might be useful.)