解:因为 x+y=2,xy=-1/2 ,x^2y+xy^2=xy(x+y)=-1/2*(2)=-1x^2+y^2=(x^2+y^2+2xy)-2xy=(x+y)^2-2xy=(2)^2-2(-1/2)=5(x-y)^2==x^2+y^2-2xy==(x^2+y^2+2xy)-4xy=(x+y)^2-4xy=(2)^2-4(-1/2)=6