Đáp án:
Giải thích các bước giải:
$\dfrac1{\sqrt5+\sqrt3}-\dfrac1{\sqrt5-\sqrt3}$
$=\dfrac{\sqrt5-\sqrt3}{(\sqrt5+\sqrt3)(\sqrt5-\sqrt3)}-\dfrac{\sqrt5+\sqrt3}{(\sqrt5+\sqrt3)(\sqrt5-\sqrt3)}$
$=\dfrac{\sqrt5-\sqrt3-\sqrt5-\sqrt3}{5-3}$
$=\dfrac{-2\sqrt3}2$
$=-\sqrt3$
Xin hay nhất!!!