1條A. Maths Compound Angles問題~10分呀~

It is a very easy questions.

Step:
1) Use cross-method to become a sin[θ+(B/2)] = c sin[θ-(B/2)].
2) Use compound angle formula.
3) Grouping the like term
4) You can find the answer.

Full solution:
c/a = sin[θ+(B/2)]/sin[θ-(B/2)]
a sin[θ+(B/2)] = c sin[θ-(B/2)]
a sinθsin(B/2) + a cosθcos(B/2) = c sinθsin(B/2) + c cosθcos(B/2)
(a-c) sinθsin(B/2) = -(a+c) cosθcos(B/2)
tanθ = [(c+a)/(c-a)]tan(B/2).