Two masses m1 and m2 (m1=m2) are connected by a rigid rod of length d and of negligible mass. An extensionless string of length l1 is attached to m1 and connected to a fixed point of support P. Similarly, a string of length l2 (l1=l2) connects m2 and P. Obtain the equation describing the motion in the plane of m1, m2, and P, and find the frequency of small oscillations around the equilibrium position.