Find grad f. Graph some level curves f = const. Indicate Vf by arrows at some points of these curves. 1. f = (x + 1)(2y 1) 2. f = 9x2 + 4y2 3. f = y/x 4. (y + 6)2 + (xr 4)2 5. f = x* + y* 6. f = (x2 - y?)/(x + y?) ,4