mx³+3nxy²+2x³-xy²+y =(m+2)x³+(3n-1)xy²+y 因为不含三次项 所以 m+2=0 m=-2 3n-1=0 n=1/3 2m+3n =2*(-2)+3*1/3 =-4+1 =-3 祝学习进步,望采纳~~