因为x+2y=0,所以x=-2y原式=(x^2+2xy)/(xy+y^2)=(4y^2-4Y^2)/(-3y^2+y^2) =0/(-2y^2)又因为xy不等于零,所以x、y君不等于零,所以-2y^2亦不等于零所以原式=0
x^2+2xy / xy+y^2=x(x+2y)/(xy+y^2)=0