Show that the field on the x axis for the dipole (negative on the right, positive on the left separated by 2a) is given by the equation E = kq / x^3 for x >>a.
Coulomb's Law F = kq1q2 / r^2
E = F/q = kQ / r^2
The Attempt at a Solution
Since its a vector sum, I just add the two equations to get E = kq / r^2 + k(-q) / r^2
The solutions manual gives me E = kq / (x-a)^2 + k(-q) / (x+a)^2
I feel stupid but I seem to be hitting a wall. Why does the positive charge have (x-a)^2, while the negative charge has a (x+a)^2? What does 'a' represent? I keep confusing myself, can someone clarify this for me? I understand everything except the nature of the denominators. Thanks