Chapter 18, Problem 19CQ

To determine

(a)

The direction of the total coulomb force on $q$ if $q$ is negative, $q_{\text{a}}=q_{\text{c}}$ and both are negative and $q_{\text{b}}=q_{\text{c}}$ and both are positive.

To determine

(b)

The direction of the electric field at the center of the square.