I think it would be better if I put the picture.
Find the direction of the electric field.
Find the magnitude of electric field due at C due to charges A, B, and D.
E = kq/r^2
The Attempt at a Solution
For the first problem, I drew vector diagrams based on the charges at the center of the square. I ended up having 4 arrows:
O -> A (electron attraction)
O -> D (electron attraction)
O -> A (proton repulsion of charge C)
O -> D (proton repulsion of charge D)
So basically I had 2 visual arrows of pointing NW and SW from the origin. This makes the direction of the electric field to be West. Thats basically the part I only got.
For the magnitude of the electric field I used E = kq/r^2 . I know r = [√(2)/2]a. Now I got lost on what to really do (I tried a bunch of stuff but it didn't really make sense to me). The final answer for the first question is 4√2 kq/a^2