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![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(\sqrt{12}-\sqrt{27}+\sqrt{3}\)
\(=2\sqrt{3}-3\sqrt{3}+\sqrt{3}\)
=0
b: \(\left(\sqrt{12}-3\sqrt{15}-4\sqrt{135}\right)\cdot\sqrt{3}\)
\(=\left(2\sqrt{3}-3\sqrt{15}-12\sqrt{15}\right)\cdot\sqrt{3}\)
\(=6-45\sqrt{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(\sqrt{12}+3\sqrt{15}-4\sqrt{135}\right)\sqrt{3}\)
\(=\left(2\sqrt{3}+3\sqrt{15}-12\sqrt{15}\right)\sqrt{3}\)
\(=\left(2\sqrt{3}-9\sqrt{15}\right)\sqrt{3}\)
\(=6-9\sqrt{45}\)
\(a.\left(\sqrt{12}+3\sqrt{15}-4\sqrt{135}\right)\sqrt{3}=\left(2\sqrt{3}+3\sqrt{15}-12\sqrt{15}\right)\sqrt{3}=2.3-9\sqrt{9.5}=6-27\sqrt{5}\) \(b.\sqrt{252}-\sqrt{700}+\sqrt{1008}-\sqrt{448}=\sqrt{36.7}-\sqrt{100.7}+\sqrt{144.7}-\sqrt{64.7}=6\sqrt{7}-10\sqrt{7}+12\sqrt{7}-8\sqrt{7}=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) Sửa đề: \(\left(\sqrt{12}+3\sqrt{5}-4\sqrt{135}\right)\cdot\sqrt{3}\)
Ta có: \(\left(\sqrt{12}+3\sqrt{5}-4\sqrt{135}\right)\cdot\sqrt{3}\)
\(=\sqrt{12}\cdot\sqrt{3}+3\sqrt{5}\cdot\sqrt{3}-4\sqrt{135}\cdot\sqrt{3}\)
\(=6+3\sqrt{15}-36\sqrt{5}\)
b) Ta có: \(\sqrt{252}-\sqrt{700}+\sqrt{1008}-\sqrt{448}\)
\(=3\sqrt{28}-5\sqrt{28}+3\sqrt{112}-2\sqrt{112}\)
\(=-2\sqrt{28}+\sqrt{112}=-\sqrt{112}+\sqrt{112}=0\)
c) Ta có: \(2\sqrt{40\sqrt{12}}-2\sqrt{\sqrt{75}}-3\sqrt{5\sqrt{48}}\)
\(=2\cdot4\cdot\sqrt{5}\cdot\sqrt{\sqrt{3}}-2\cdot\sqrt{5}\cdot\sqrt{\sqrt{3}}-3\cdot2\cdot\sqrt{5}\cdot\sqrt{\sqrt{3}}\)
\(=8\sqrt{5}\cdot\sqrt{\sqrt{3}}-2\sqrt{5}\sqrt{\sqrt{3}}-6\sqrt{5}\sqrt{\sqrt{3}}\)
=0
Bài 2:
a) Ta có: \(A=\frac{\sqrt{6}+\sqrt{14}}{2\sqrt{3}+\sqrt{28}}\)
\(=\frac{\sqrt{2}\left(\sqrt{3}+\sqrt{7}\right)}{2\left(\sqrt{3}+\sqrt{7}\right)}\)
\(=\frac{1}{\sqrt{2}}\)
b) Ta có: \(B=\frac{9\sqrt{5}+3\sqrt{27}}{\sqrt{5}+\sqrt{3}}\)
\(=\frac{\sqrt{405}+\sqrt{243}}{\sqrt{5}+\sqrt{3}}\)
\(=\frac{9\left(\sqrt{5}+\sqrt{3}\right)}{\sqrt{5}+\sqrt{3}}=9\)
c) Ta có: \(C=\frac{3\sqrt{8}-2\sqrt{12}+\sqrt{20}}{3\sqrt{18}-2\sqrt{27}+\sqrt{45}}\)
\(=\frac{\sqrt{72}-\sqrt{48}+\sqrt{20}}{\sqrt{162}-\sqrt{108}+\sqrt{45}}\)
\(=\frac{2\left(\sqrt{18}-\sqrt{12}+\sqrt{5}\right)}{3\left(\sqrt{18}-\sqrt{12}+\sqrt{5}\right)}=\frac{2}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
c.√252−√700+√1008−√448
\(=6\sqrt{7}-10\sqrt{7}+12\sqrt{7}-8\sqrt{7}\)
=(6-10+12-8)\(\sqrt{7}\)
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=2\sqrt{80\sqrt{3}}+3\sqrt{20\sqrt{3}}-2\sqrt{5\sqrt{3}}-4\sqrt{45\sqrt{3}}\)
\(=8\sqrt{5\sqrt{3}}+6\sqrt{5\sqrt{3}}-2\sqrt{5\sqrt{3}}-12\sqrt{5\sqrt{3}}\)
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(E=2\sqrt{40\sqrt{12}}+3\sqrt{5\sqrt{48}}-2\sqrt{\sqrt{75}}-4\sqrt{15\sqrt{27}}.\)
\(=8\sqrt{5\sqrt{3}}+6\sqrt{5\sqrt{3}}-2\sqrt{5\sqrt{3}-12\sqrt{5\sqrt{3}}}\)
\(=0\)
b) \(F=\frac{1}{\sqrt{3}}+\frac{1}{3\sqrt{2}}+\frac{1}{\sqrt{3}}\sqrt{\frac{5}{12}-\frac{1}{\sqrt{6}}}.\)
Vì \(=\frac{5}{12}-\frac{1}{\sqrt{6}}=\frac{5-2\sqrt{6}}{12}=\frac{\left(\sqrt{3}-\sqrt{2}\right)^2}{12}\)
\(\frac{1}{\sqrt{3}}+\frac{1}{2\sqrt{3}}=\frac{\sqrt{3}}{3}+\frac{\sqrt{2}}{6}=\frac{2\sqrt{3}+\sqrt{2}}{6}\)
Nên \(F=\frac{2\sqrt{3}+\sqrt{2}}{6}+\frac{1}{\sqrt{3}}\sqrt{\frac{\left(\sqrt{3}-\sqrt{2}\right)^2}{12}}=\frac{2\sqrt{3}+\sqrt{2}+\sqrt{3}-\sqrt{2}}{6}=\frac{3\sqrt{3}}{6}=\frac{\sqrt{3}}{2}\)
a)\(\sqrt{39}-27\sqrt{5}\)
b)0