If an external force having frequency near that of oscillation is applied to sucessively to parametric excitation circuit, the osci1lation of n/2-harmonic components may easily disappear depending upon circumstances. In the previous paper, the phenomenon of vibration disappearance of 3/2-harmonicoscillation was analytically explained by adding a term of the external force to a nonlinearized Mathieu equation and assuming the frequency components of 1/2-, 3/2-harmonic and external force. As the relations with respect to amplitudes derived by the method of harmonic balance become simultaneous equations of high degrees, we used an approximation in order to investigate this phenomenon easily. This paper discusses the results obtained by this approximation in comparison with the numericnl solutions of the above simultaneous equations. It is shown that close agreement between them is obtained.
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