If $a = 13$, $b = 14$, $c = 15$ then find the value of $\tan \frac{c}{2}$ —

Explanation

$s = \frac{a+b+c}{2}$ $= \frac{13+14+15}{2}$ $s = 21$ $\tan \frac{c}{2} = \sqrt{\frac{(s-a)(s-b)}{s(s-c)}}$ $= \sqrt{\frac{(21-13)(21-14)}{21(21-15)}} = \frac{2}{3}$