Đáp án:
`A=(4\sqrt{a}(2-a))/(a-1)`
Giải thích các bước giải:
`A=(\sqrt{a}+1)/(\sqrt{a}-1)-(\sqrt{a}-1)/(\sqrt{a}+1)-4\sqrt{a}`
`=((\sqrt{a}+1)(\sqrt{a}+1))/((\sqrt{a}-1)(\sqrt{a}+1))-((\sqrt{a}-1)(\sqrt{a}-1))/((\sqrt{a}+1)(\sqrt{a}-1))-4\sqrta`
`=(a+\sqrt{a}+\sqrt{a}+1)/(a-1)-(a-\sqrt{a}-\sqrt{a}+1)/(a-1)-4\sqrt{a}`
`=(a+2\sqrt{a}+1-a+2\sqrt{a}-1)/(a-1)-4\sqrt{a}`
`=(4\sqrt{a})/(a-1)-4\sqrt{a}`
`=(4\sqrt{a})/(a-1)-(4\sqrt{a}(a-1))/(a-1`
`=(4\sqrt{a}-4\sqrt{a}(a-1))/(a-1)`
`=(4\sqrta-4a\sqrta+4\sqrta)/(a-1)`
`=(8\sqrta-4a\sqrta)/(a-1)`
`=(4\sqrta(2-a))/(a-1)`
Vậy `A=(4\sqrt{a}(2-a))/(a-1)`
