In a certain two-dimensional field of force the potential energy of a particle has the form \(U=\alpha x^{2}+\beta y^{2}\), where \(\alpha\) and \(\beta\) are positive constants whose magnitudes are different. Find out: (a) whether this field is central; (b) what is the shape of the equipotential surfaces and also of the surfaces for which the magnitude of the vector of force \(F=\) const.