Find the transfer function from the input force f(t) to the displacement x1. Here, X1 and X2 are the displacements of the masses M₁ and M₂ from the equilibrium positions of the system. They are absolute coordinates, i.e. measured relative to something fixed. Assume the floor beneath the masses is frictionless. x₁(1) x₂(1) C f(1) K₁ K3 0000 M₁ K₁₂ M 0000 0000