SUMMARYThe stable periodic motion, described by Rayleigh di erential equation, is solved by using the Mathematica software system. We deÿne rules computing the periods T , the magnitude A, the displacement u(t), and the velocity v(t) for prescribed perturbation parameter and circular frequency !. These rules have been explored to ÿnd the period T , the magnitude A, and the reducing factor of the circular frequency = 2 =T with 10 correct digits after decimal point for ! equal to 1 and the values of in the range from 0.1 to 100. The displacement and the velocity are plotted for equal to 0.1, 1, 10, and 100.