Đáp án + giải thích các bước giải:
`\sqrt{20-\sqrt{384}}-\sqrt{56-8\sqrt{24}}`
`=\sqrt{20-\sqrt{64.6}}-\sqrt{56-8\sqrt{4.6}}`
`=\sqrt{20-8\sqrt{6}}-\sqrt{56-16\sqrt{6}}`
`=\sqrt{12-2.2\sqrt{2}.2\sqrt{3}+8}-\sqrt{48-2.4\sqrt{3}.2\sqrt{2}+8}`
`=\sqrt{(\sqrt{12}-\sqrt{8})^2}-\sqrt{(\sqrt{48}-\sqrt{8})^2}`
`=|\sqrt{12}-\sqrt{8}|-|\sqrt{48}-\sqrt{8}|`
`=\sqrt{12}-\sqrt{8}-\sqrt{48}+\sqrt{8}`
`=\sqrt{12}-\sqrt{48}`
`=\sqrt{4.3}-\sqrt{16.3}`
`=2\sqrt{3}-4\sqrt{3}`
`=-2\sqrt{3}`