Consider the function of two variables f(x, y) = 1. if (x, y) approaches (0, 0) along the x-axis, then what is the limit? 2. if (x, y) approaches (0. 0) along the y-axis, then what is the limit? 3. Determine wheter does exist or not. 4. If f(x, y, z) = xsinyz, (a) find the gradient of f and (b) find the directional derivative of f at P(1, 3, 0) in the direction of v = i + 2j - k