sin 650=cos 350
\(cos70^0=sin30^0\)
\(tan80^0=cot20^0\)
\(cot68^0=tan32^0\)
bài 3
a) \(tana=\dfrac{sina}{cosa}\)
\(\dfrac{AC}{\dfrac{BC}{\dfrac{AB}{BC}}}=\dfrac{AC}{AB}=tana\)
b) tan a.cot a=1
\(\dfrac{AC}{AB}.\dfrac{AB}{AC}=1\)
Bài 2:
\(\sin65^0=\cos25^0\)
\(\cos70^0=\sin20^0\)
\(\tan80^0=\cot10^0\)
\(\cot68^0=\tan22^0\)