Charge +Q = +7.10 nC is uniformly distributed along the right half of a thin rod bent into a semicirle of radius R = 3.60 cm, while charge −Q = −7.10 nC is uniformly distributed along the left half of the rod. What is the magnitude and direction of the electric field at point P, the centre of the circle?

Answer 1

http://www.phys.uri.edu/gerhard/PHY204/tsl329.pdf
Then double that.

Answer 2

I don't get it