Nhận dạng tam giác $ABC$ biết
1) $\frac{1}{\sin A}+\frac{1}{\sin B}=\frac{2}{\cos \frac{C}{2}}$
2) $\left ( \tan \frac{A}{2}+\tan \frac{B}{2} \right )^2+\left ( \cot \frac{A}{2}+\cot \frac{B}{2} \right )^2=8$
3) $3S=2R^2.\sum \sin^3 A$
4) $\sum \frac{1}{\sin A}=\sum \frac{1}{\cos \frac{A}{2}}$
5) $\sum \frac{1}{\cos A}=\sum \frac{1}{\sin \frac{A}{2}}$ (tam giác nhọn)
6) $\sum \frac{1}{\cot A+\cot B}=\sum \sin A$
7) $\sum \sqrt{\sin A}=\sum \sqrt{\cos \frac{A}{2}}$
8) $\sum \sqrt[3]{\sin A}=\sum \sqrt[3]{\cos \frac{A}{2}}$
9) $\sum \frac{\sin A}{m_a}=\sqrt{3}$ $(R=1)$
10) $\sum \frac{1}{2+\cos 2A}=\frac{5}{6}$