What is the the electric field at a point midway between a -7.79 uC and a +5.66 uC charge 3.74 cm apart? Take the direction towards the positive charge to be positive.
So I did:
(9E9)(-7.79E-6)/(.00187^2)
and
(9E9)(5.66E-6)/(.00187^2)
then added the two answers together, which...
I'm working on this problem also, and getting something wrong. I'm using the same equation as you. Did you find that dividing r/2 gave you the correct answer?