Rút gọn A :
`A=(\sqrt{12}+2\sqrt{27}).\sqrt{3}/2-\sqrt{200}/\sqrt{2}`
`=(2\sqrt{3}+6\sqrt{3}).\sqrt{3}/2-10`
`=8\sqrt{3}. \sqrt{3}/2-10`
`=4.3-10`
`=2`
Rút gọn B :
`B=(\sqrt{x}/(\sqrt{x}-2)+\sqrt{x}/(\sqrt{x}+2)).(x-4)/\sqrt{9x}`
`=(\sqrt{x}(\sqrt{x}+2)+\sqrt{x}(\sqrt{x}-2))/((\sqrt{x}-2)(\sqrt{x}+2)).((\sqrt{x}-2)(\sqrt{x}+2))/\sqrt{9x}`
`=(x+2\sqrt{x}+x-2\sqrt{x})/\sqrt{9x}`
`=(2x)/(3\sqrt{x})`
`=(2\sqrt{x})/3`
`A>B`
`->2>(2\sqrt{x})/3`
`->(2\sqrt{x})/3<2`
`->(2\sqrt{x}-6)/3<0`
`->2\sqrt{x}-6<0`
`->2\sqrt{x}<6`
`->\sqrt{x}<3`
`->x<9`
