Đáp án:
`a)` `{ 1-2\sqrt{a}+a}/{1-a}`
`b)` `{\sqrt{a}+\sqrt{b}+1}/{a+b}`
Giải thích các bước giải:
`a)` `{1-\sqrt{a}}/{1+\sqrt{a}}` `(a\ge 0; a\ne 1)`
`={(1-\sqrt{a})^2}/{(1+\sqrt{a})(1-\sqrt{a})}`
`={1-2\sqrt{a}+a}/{1^2-(\sqrt{a})^2}`
`={1-2\sqrt{a}+a}/{1-a}`
$\\$
`b)` `1/{\sqrt{a}+\sqrt{b}-1}` `\quad (a>0;b>0; ab=1/4)`
`={1.(\sqrt{a}+\sqrt{b}+1)}/{(\sqrt{a}+\sqrt{b}-1)(\sqrt{a}+\sqrt{b}+1)}`
`={\sqrt{a}+\sqrt{b}+1}/{(\sqrt{a}+\sqrt{b})^2-1^2}`
`={\sqrt{a}+\sqrt{b}+1}/{a+2\sqrt{ab}+b-1}`
`={\sqrt{a}+\sqrt{b}+1}/{a+2. \sqrt{1/4}+b-1}`
`={\sqrt{a}+\sqrt{b}+1}/{a+1+b-1}`
`={\sqrt{a}+\sqrt{b}+1}/{a+b}`
