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![](https://rs.olm.vn/images/avt/0.png?1311)
cot710 = tan190; cot690 = tan = 210
=> tan190 < tan210 < tan280 < tan390 < tan420
=> cot710 < cot690 < tan280 < tan390 < tan420
\(a,\cot71^0=\tan19^0< \cos69^015'=\tan20^045'< \tan28^0< \tan38^0< \tan42^0\\ b,\cos79^013'=\sin10^047'< \sin32^0< \sin38^0< \cos51^0=\sin39^0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\dfrac{2}{\sqrt{17}+\sqrt{19}}\) ; \(B=\dfrac{2}{\sqrt{19}+\sqrt{21}}\)
Mà \(0< \sqrt{17}+\sqrt{19}< \sqrt{19}+\sqrt{21}\)
\(\Rightarrow\dfrac{2}{\sqrt{17}+\sqrt{19}}>\dfrac{2}{\sqrt{19}+\sqrt{21}}\)
\(\Rightarrow A>B\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(3\sqrt{3}=\sqrt{27}mà\sqrt{27}< \sqrt{29}=>3\sqrt{3}< \sqrt{29}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\sin39^013'=0,6322\)
\(\cos52^018'=0,6115\)
\(\tan13^020'=0,2370\)
\(\cot10^017'=5,5118\)
\(\sin54^0=0,8090\)
\(\cos45^0=0,7071\)
![](https://rs.olm.vn/images/avt/0.png?1311)
bằng nhau nhé
Sin 39=Cos51
Chúc bạn học tốt!!!