【摘要】 考虑正负系数中立型时滞微分方程（x（t）-P（t）x（t-τ））’＋Q（t）x（t-σ）－R（t）x（t-γ）＝0（*）本文获得了方程（*）存在有界正解的充分必要条件，本文结果回答了文献[1]中的公开问题3。更多还原

【Abstract】 Consider the neutral differential equtions with positive and negative coeffic ie nt sWe obtain a necessary and sufficient condition for the existence of bounded positive solutionsof Eq (* ),an open problem in the literature [fi is answered.更多还原