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J
21 tháng 4 2019
a) \(\frac{2}{3}\sqrt{3}-\frac{1}{4}\sqrt{18}+\frac{2}{5}\sqrt{2}-\frac{1}{4}\sqrt{12}\)
\(=\frac{2}{3}\sqrt{3}-\frac{1}{4}\sqrt{2\times3^2}+\frac{2}{5}\sqrt{2}-\frac{1}{4}\sqrt{3\times2^2}\)
\(=\frac{2}{3}\sqrt{3}-\frac{3}{4}\sqrt{2}+\frac{2}{5}\sqrt{2}-\frac{1}{2}\sqrt{3}\)
\(=\frac{1}{6}\sqrt{3}-\frac{7}{20}\sqrt{2}=\frac{10\sqrt{3}-21\sqrt{2}}{60}\)
b) \(\left(\sqrt{10}+\sqrt{2}\right)\left(6-2\sqrt{5}\right)\sqrt{3+\sqrt{5}}\)
\(=\sqrt{2}\left(\sqrt{5}+1\right)\left(5-2\sqrt{5}\times1+1\right)\sqrt{3+\sqrt{5}}\)
\(=\left(\sqrt{5}+1\right)\left(\sqrt{5}-1\right)^2\sqrt{6+2\sqrt{5}}\)
\(=4\left(\sqrt{5}-1\right)\sqrt{5+2\sqrt{5}\times1+1}\)
\(=4\left(\sqrt{5}-1\right)\sqrt{\left(\sqrt{5}+1\right)^2}=4\left(\sqrt{5}-1\right)\left(\sqrt{5}+1\right)\)
\(=4^2=16\)
ND
26 tháng 7 2018
*\(A=\sqrt{6-2\sqrt{5}}-\sqrt{6+2\sqrt{5}}=\sqrt{\left(\sqrt{5}-1\right)^2}-\sqrt{\left(\sqrt{5}+1\right)^2}=\sqrt{5}-1-\sqrt{5}+1=2\)
\(\Rightarrow A\in Z\)
* \(B=\dfrac{\sqrt{3-2\sqrt{2}}}{\sqrt{17-2\sqrt{2}}}-\dfrac{\sqrt{3+2\sqrt{2}}}{\sqrt{17+12\sqrt{2}}}\) \(=\dfrac{\sqrt{\left(\sqrt{2}-1\right)^2}}{\sqrt{\left(3-2\sqrt{2}\right)^2}}-\dfrac{\sqrt{\left(\sqrt{2}+1\right)^2}}{\sqrt{\left(3+2\sqrt{2}\right)^2}}\) \(=\dfrac{\sqrt{2}-1}{3-2\sqrt{2}}-\dfrac{\sqrt{2}+1}{3+2\sqrt{2}}\)
\(=\dfrac{\left(\sqrt{2}-1\right)\left(3+2\sqrt{2}\right)-\left(\sqrt{2}+1\right)\left(3-2\sqrt{2}\right)}{\left(3-2\sqrt{2}\right)\left(3+2\sqrt{2}\right)}\) \(=\dfrac{3\sqrt{2}+4-3-2\sqrt{2}-3\sqrt{2}+4-3+2\sqrt{2}}{9-8}\)
\(=2\)
\(\Rightarrow B\in Z\)
17 tháng 9 2016
\(\sqrt{\sqrt{5-\sqrt{3-\sqrt{29-12\sqrt{5}}}}}=\sqrt{\sqrt{5-\sqrt{3-\sqrt{\left(2\sqrt{5}-3\right)^2}}}}\)
\(=\sqrt{\sqrt{5-\sqrt{3-\left(2\sqrt{5}-3\right)}}}=\sqrt{\sqrt{5-\sqrt{6-2\sqrt{5}}}}=\sqrt{\sqrt{5-\sqrt{\left(\sqrt{5}-1\right)^2}}}\)
\(=\sqrt{\sqrt{5-\left(\sqrt{5}-1\right)}}=\sqrt{\sqrt{6-\sqrt{5}}}\)
H9
HT.Phong (9A5)
CTVHS
21 tháng 7 2023
a) \(\sqrt{\dfrac{3-\sqrt{5}}{3+\sqrt{5}}}\)
\(=\sqrt{\dfrac{\left(3-\sqrt{5}\right)^2}{\left(3+\sqrt{5}\right)\left(3-\sqrt{5}\right)}}\)
\(=\dfrac{\sqrt{\left(3-\sqrt{5}\right)^2}}{\sqrt{3^2-\left(\sqrt{5}\right)^2}}\)
\(=\dfrac{\left|3-\sqrt{5}\right|}{\sqrt{9-5}}\)
\(=\dfrac{3-\sqrt{5}}{2}\)
b) \(\sqrt{\dfrac{2-\sqrt{3}}{2+\sqrt{3}}}\)
\(=\sqrt{\dfrac{\left(2-\sqrt{3}\right)^2}{\left(2+\sqrt{3}\right)\left(2-\sqrt{3}\right)}}\)
\(=\dfrac{\sqrt{\left(2-\sqrt{3}\right)^2}}{\sqrt{2^2-\left(\sqrt{3}\right)^2}}\)
\(=\dfrac{\left|2-\sqrt{3}\right|}{\sqrt{4-3}}\)
\(=\dfrac{2-\sqrt{3}}{1}\)
\(=2-\sqrt{3}\)
21 tháng 7 2023
a: \(=\sqrt{\dfrac{\left(3-\sqrt{5}\right)\left(3-\sqrt{5}\right)}{4}}=\dfrac{3-\sqrt{5}}{2}\)
b: \(=\sqrt{\dfrac{\left(2-\sqrt{3}\right)^2}{1}}=2-\sqrt{3}\)
d: \(=\left(-3+3\sqrt{6}+4+2\sqrt{6}-12-4\sqrt{6}\right)\left(\sqrt{6}+11\right)\)
=(căn 6-11)(căn 6+11)
=6-121=-115
25 tháng 1 2023
\(=\sqrt{2-\sqrt{3}}-\sqrt{2+\sqrt{3}}\)
\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{4-2\sqrt{3}}-\sqrt{4+2\sqrt{3}}\right)\)
\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{3}-1-\sqrt{3}-1\right)=-2\cdot\dfrac{\sqrt{2}}{2}=-\sqrt{2}\)