Answer and Explanation:
The reason for the not being perfectly spherical ad bulging out at the equator is that The centripetal force acting toward's the earth gravitational center tries to keep the Earth in perfect spherical shape.
Also the angular momentum of the orbiting planet influences the bulge,
The greater angular momentum results in more bulge while the lower value of it results in lesser bulge and more perfect spherical shape.
Also, a greater amount of force directed towards the center and acting on the object at the equator results in the bulges at the equator whereas at poles this force is not required and hence radius is lower in that region.