Physics- Find the electric force?

Question

Point charges +Q and -2Q are separated by a distance d. A point charge q is equidistant from these charges at a distance x from their midpoint. What is the electric force on q?

Answer 1

Find the two force vectors and sum them.

Each vector will have |r| = sqrt((d/2)^2+x^2), and |F1| = kqQ/r^2 and |F2| = 2kqQ/r^2. Find the components of F1 and F2 trigonometrically from r, d/2 and x, keeping in mind polarity and direction. q is repelled by one and attracted by the other. The two X forces will thus have the same polarity and the Y forces will be of opposite polarity.