Find the circulation of the field F = yi + (x + 2y) j around each of the following closed curves (in counterclockwise direction). (a) Closed curve formed by four end-to-end line segments: (1, -1) to (1, 1), (1, 1) to (-1, 1), (-1, 1) to (-1, -1), and (-1, -1) to (1, -1). (b) x2 + 1 = a', where a is an arbitrary positive real number