In any triangle ABC, we have to show that
(i) (ii)
(iii)
(i) R.H.S. =
[∵ b sinC = c sinB]
[By sine formula]
= - cos(B + C) [∵ k sin B = b]
= - cos ( - A)
= cos A = L.H.S.
Similarly, we can show (ii) and (iii)