Four protons, each with charge +e, are fixed at the corners of a square of side length a. The square is in the +x, +yquadrant of the xy plane with one corner at the origin. Find the magnitude and direction of the electric field E at
(a) the center of the square,
(b) the point (a/2, 0), and
(c) the point (-a, -a).
In each case state which protons contribute to the net electric field you compute and which cancel, and draw a diagram showing the individual electric field vectors due to each proton at the point in question.