Necessary and Sufficient Conditions for Oscillations of Neutral Delay Equations with Several Positive and Negative Coefficients

In thisPositive and (l)PaPer,we eonsider thenegative eoeffieients ofoseillations of neutral delay equations with、o山 the form·习k-1十玄。,·(卜r。卜全·,·(卜。,))十 XZ夕.、、d一dtJ.。、x(‘一u、)一名h:x(‘一。:)=o,where the eoeffieients and the delays areequation of(1)15non一negative constants.The Charaeteri“tieN(2)F(几):=‘+‘习。‘e一“·卜‘习r,e一‘’,+习。、e一“”一习h:e一‘’一0. ‘二lj一1论一15,1 our main result 19 the following theorem. Theorem All solutions of(l)oseillate if …