方程（dx）/（dt）＝φ（y）－F（x），（dy）/（dt）＝－g（x）的极限环存在定理

A Existence Theorem of Limit Cycle of Equation dxdt=φ(y)-F(x),dydt=-g(x)

讨论了非线性微分方程ｄｘｄｔ＝φ（ｙ）－Ｆ（ｘ），ｄｘｄｔ＝－ｇ（ｘ）极限环的存在性。

This paper discusses existence of limit cycle of the nolinear differential equation dxdt=φ(y)-F(x),dydt=-g(x) and has obtained improved existence theorem of limit cycle.