Suppose f(:r,y) = nary + bar, where a and b are two real numbers. Let u = (l, 1) and v = (1,0). Suppose that the directional derivative of f at the point (1, 1) in the direction of u is \\/ and that the directional derivative of f at the point (1,1) in the direction of v is 3. Use this information to nd the values of a and b and then nd all unit vectors w such that the directional derivative of f at the point (1, 1) in the direction of w is 0