Four protons are placed at the corners of a square of side length a = 1.0 angstrom. The square is in the +x, +y quadrant of the xy plane with one corner at the origin. Find the electric field magnitude and direction (a) at the center of the square, (b) at the point (-a, -a), and (c) at the point (1/2a, 0). In each case state which protons contribute to the field you compute and which cancel.