( √a +√b/√a-√b – √a-√b/√a+√b) (a-b) Ai giúp em với ạ em cam rơn

( $\frac{\sqrt[]{a}+\sqrt[]{b}}{\sqrt[]{a}-\sqrt[]{b}}$- $\frac{\sqrt[]{a}-\sqrt[]{b}}{\sqrt[]{a}+\sqrt[]{b}}$).( a-b)

= $\frac{(\sqrt[]{a}+\sqrt[]{b})^{2}-(\sqrt[]{a}-\sqrt[]{b})^{2}}{(\sqrt[]{a}-\sqrt[]{b}).(\sqrt[]{a}+\sqrt[]{b})}$.( a-b)

= $\frac{4.\sqrt[]{ab}}{a-b}$.(a-b)

= $4.\sqrt[]{ab}$