計算二
\(\displaystyle \frac{A}{2}+\frac{B}{2}+\frac{C}{2}=\frac{\pi}{2} \)
\(\displaystyle tan \frac{A}{2} tan \frac{B}{2} + tan \frac{A}{2} tan \frac{C}{2}+ tan \frac{B}{2} tan \frac{C}{2}=1 \)
\(\displaystyle tan \frac{A}{2} tan \frac{B}{2} + tan \frac{B}{2} tan \frac{C}{2}=\frac{2}{3}=2 tan \frac{A}{2} tan \frac{C}{2} \)
\(\displaystyle cot \frac{C}{2}+cot \frac{A}{2}=2 cot \frac{B}{2} \)
\(\displaystyle \frac{s-c}{r}+\frac{s-a}{r}=2 \frac{s-b}{r} \)
\(\displaystyle a+c=2b \)