> How does one derive
> tan(A/2) = sqrt[(s-b)(s-c)/{s(s-a)}]?
>
> Thanks.
What did you mean with A,a,b,c, and s?
It is usual to us if there is a triangle ABC,
a is the side in front of angle A,
b is the side in front of angle B,
c is the side in front of angle C
And s=(a+b+c)/2.
Was what you meant as above?