Đáp án + giải thích các bước giải:
6/ `a>=0;a\ne 1/4`
`(\sqrt{a}-2a)/(2\sqrt{a}-1)`
`=(\sqrt{a}(1-2\sqrt{a}))/(-(1-2\sqrt{a}))`
`=\sqrt{a}/(-1)`
`=-\sqrt{a}`
7/ `x\ne\sqrt{2}`
`(x^2-2)/(x-\sqrt{2})`
`=((x-\sqrt{2})(x+\sqrt{2}))/(x-\sqrt{2})`
`=x+\sqrt{2}`
8/ `x>=0;x\ne9`
`(\sqrt{x}-3)/(x-9)`
`=(\sqrt{x}-3)/((\sqrt{x}-3)(\sqrt{x}+3))`
`=1/(\sqrt{x}+3)`
9/ `x;y>=0;x\ney`
`(x+\sqrt{x}\sqrt{y})/(x-y)`
`=(\sqrt{x}(\sqrt{x}+\sqrt{y}))/((\sqrt{x}-\sqrt{y})(\sqrt{x}+\sqrt{y}))`
`=\sqrt{x}/(\sqrt{x}-\sqrt{y})`
10/ `x;y>=0`
`(x\sqrt{y}+y\sqrt{x})/(x+2\sqrt{xy}+y)`
`=(\sqrt{x}\sqrt{y}(\sqrt{x}+\sqrt{y}))/(\sqrt{x}+\sqrt{y})^2`
`=\sqrt{xy}/(\sqrt{x}+\sqrt{y})`
