若x不等于y，试比较x^3+13x(y^2)与5(x^2)y+9y^3的大小。希望有详细的解答，谢谢
热心网友
x^3+13x(y^2)-5(x^2)y-9y^3=x^2(x-y)-4xy(x-y)+9y^2(x-y)==[x^2-4xy+9y^2](x-y)=[(x-2y)^2+5y^2](x-y)=1.[(x-2y)^2+5y^2]=0x=y=0.若x不等于y==(x-2y)^2+5y^202.xy==x^3+13x(y^2)5(x^2)y+9y^33.xx^3+13x(y^2)<5(x^2)y+9y^3.