The first term of L.H.S. IS sin(B−C)cosBcosC=sinBcosC−cosBsinCcosBcosC=sinBcosCcosBcosC−cosBsinCcosBcosC=tanB−tanC
Similarly, the second term of L.H.S. is (tanC−tanA)
and the third term of the L.H.S. is (tanA−tanB)
Now L.H.S.=(tanB−tanC)+(tanC−tanA)+(tanA−tanB)=0
Ans: 0