Cho ba biểu thức P = x sqrt y + y sqrt x ; Q = x sqrt x + y sqrt y ; R = x - y

$P=x \sqrt{y}+y \sqrt{x}$ !!$=(\sqrt{x})^{2} \sqrt{y}+(\sqrt{y})^{2} \sqrt{x}$ !!$=\sqrt{x y}(\sqrt{x}+\sqrt{y})$ !!$Q=$ !!$x \sqrt{x}+y \sqrt{y}=(\sqrt{x})^{3}+(\sqrt{y})^{3}$ !!$=(\sqrt{x}+\sqrt{y})(x-\sqrt{x y}+y)$ !!$R=x-y$ !!$=(\sqrt{x})^{2}-(\sqrt{y})^{2}$ !!$=(\sqrt{x}-\sqrt{y})(\sqrt{x}+\sqrt{y})$ !!Vậy $R=(\sqrt{x}-\sqrt{y})(\sqrt{x}+\sqrt{y})$