Four weightless rods of length l each are connected by hinged joints and form a rhomb (Fig). A hinge A is fixed, and a load is suspended to a hinge C. Hinges D and B are connected by a weightless spring of length `1.5l` in the undeformed state. In equilibrium, the rods form angles `alpha_(0) = 30^(@)` with the vertical. Determine the period T of small oscillations of the load.