因为不含三次,则 mx^3+3nxy^2-2x^3-xy^2+2x+y =(m-2)x^3+(3n-1)xy^2+2x+y m-2=0 3n-1=0 m=2 n=1/3 2m+3n=2*2+3*1/3=4+1=5
