Number 12.24 Please help me

12.24. A mass m is suspended by a string of length I from a support S and oscillates as a pendulum in a vertical plane containing the X-axis and making an angle 0 with the vertical, as shown in Fig. P12.24. The support S slides back and forth along a horizontal X-axis according to the equa- tion x = a os wr. Set up Lagrange's equaions. Show that for small values of 9 the system behaves as a fored harmonic oscillator. Figure P12.24