Đáp án+giải thích các bước giải:
$\sqrt{18}-\dfrac{1}{2}\sqrt{48}-\sqrt{8}+\dfrac{4-5\sqrt{2}}{5-2\sqrt{2}}$
$=3\sqrt{2}-\dfrac{1}{2}.4\sqrt{3}-2\sqrt{2}+\dfrac{(4-5\sqrt{2})(5+2\sqrt{2})}{5^2-(2\sqrt{2})^2}$
$=3\sqrt{2}-2\sqrt{3}-2\sqrt{2}+\dfrac{(4-5\sqrt{2})(5+2\sqrt{2})}{17}$
$=\dfrac{51\sqrt{2}}{17}-\dfrac{34\sqrt{3}}{17}-\dfrac{34\sqrt{2}}{17}+\dfrac{(4-5\sqrt{2})(5+2\sqrt{2})}{17}$
$=\dfrac{51\sqrt{2}-34\sqrt{3}-34\sqrt{2}+20+8\sqrt{2}-25\sqrt{2}-20}{17}$
$=\dfrac{-34\sqrt{3}}{17}$
$=-2\sqrt{3}$
