Đáp án + Giải thích các bước giải:
`a)`
`5\sqrt{12}-\sqrt{27}+3\sqrt{48}-9\sqrt{3}`
`=5\sqrt{4}.\sqrt{3}-\sqrt{9}.\sqrt{3}+3\sqrt{16}.\sqrt{3}-9\sqrt{3}`
`=5.2.\sqrt{3}-3.\sqrt{3}+3.4.\sqrt{3}-9\sqrt{3}`
`=10\sqrt{3}-3\sqrt{3}+12\sqrt{3}-9\sqrt{3}`
`=(10-3+12-9).\sqrt{3}`
`=10\sqrt{3}`
`b)`
`((\sqrt{14}-\sqrt{7})/(\sqrt{2}-1)-(\sqrt{15}-\sqrt{5})/(1-\sqrt{3})):(2)/(\sqrt{7}-\sqrt{5})`
`=((\sqrt{7}(\sqrt{2}-1))/(\sqrt{2}-1)+(\sqrt{5}(\sqrt{3}-1))/(\sqrt{3}-1)).(\sqrt{7}-\sqrt{5})/(2)`
`=(\sqrt{7}+\sqrt{5}).(\sqrt{7}-\sqrt{5})/(2)`
`=((\sqrt{7}+\sqrt{5})(\sqrt{7}-\sqrt{5}))/(2)`
`=(7-5)/(2)`
`=(2)/(2)=1`
