rút gọn biểu thức
$(\sqrt{a}-\sqrt{b})/(\sqrt[4]{a}-\sqrt[4]{b})-(\sqrt{a}+\sqrt[4]{ab})/(\sqrt[4]{a}+\sqrt[4]{b})$
2,$\frac{a-b}{\sqrt[3]{a}-\sqrt[3]{b}}-\frac{a+b}{\sqrt[3]{a}+\sqrt[3]{b}}$
3,($\left ( \frac{a+b}{\sqrt[3]{a}+\sqrt[3]{b}}-\sqrt[3]{ab} \right ):\left ( \sqrt[3]{a}-\sqrt[3]{b} \right )^{2}$