Question

In triangle ABC, if a=16,b=24 and c=20,then cosB/2

Answer 1

$B =  \cos^{-1} {\frac{a^2+c^2-b^2}{2ca}= 82.819$

$So, \frac{B}{2} =\frac{82.819}{2}= 41.4095$

$\cos \frac{B}{2} =\cos 41.4095=0.75$