cvfbhm,

Xin lỗi em ko biết làm , em vẫn chưa lên lớp 9

1)\(\left(\frac{1}{a-\sqrt{a}}+\frac{1}{\sqrt{a}-1}\right):\frac{\sqrt{a}+1}{a-2\sqrt{a}+1}\)

\(=\left(\frac{1}{\sqrt{a}\left(\sqrt{a}-1\right)}+\frac{\sqrt{a}}{\sqrt{a}\left(\sqrt{a}-1\right)}\right)\cdot\frac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\)

\(=\frac{\sqrt{a}+1}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\frac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\)

\(=\frac{\sqrt{a}-1}{\sqrt{a}}\)

\(\sqrt{12}-2\sqrt{48}+\frac{7}{5}\sqrt{75}\)

=\(2\sqrt{3}-8\sqrt{3}+7\sqrt{3}\)

\(\sqrt{3}\)

\(\frac{1}{3}-\sqrt{7}-\frac{1}{3}+\sqrt{7}=0\)

1)(1a−√a+1√a−1):√a+1a−2√a+1(1a−a+1a−1):a+1a−2a+1

=(1√a(√a−1)+√a√a(√a−1))⋅(√a−1)2√a+1=(1a(a−1)+aa(a−1))⋅(a−1)2a+1

=√a+1√a(√a−1)⋅(√a−1)2√a+1=a+1a(a−1)⋅(a−1)2a+1

=√a−1√a

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\(\sqrt{5}-17\sqrt{3}\)

\(4\sqrt{12}-3\sqrt{45}-5\sqrt{75}+2\sqrt{125}\\ =8\sqrt{3}-9\sqrt{5}-25\sqrt{3}+10\sqrt{5}\\ \sqrt{5}-17\sqrt{3}\)

\(\sqrt{4}+\sqrt{15}-\sqrt{4}-\sqrt{15}-\sqrt{2}-\sqrt{3}\)

\(=-\sqrt{3}-\sqrt{2}\)