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Let u = (u1, u2) E R be a unit vector and let f : R - R be defined by 7 3 f (x, y) = x2 + 14' if ( x, y) # (0, 0) 0, if (x, y) = (0, 0) (a) Find the directional derivative D. f(a, b) for (a, b) # (0, 0) (b) Find Duf(0, 0). (c) Using your solution to (b), find fx(0, 0) and fy (0, 0)