In any ΔABC, prove that.
a(sin B−sin C)+b (sin C−sin A)+c (sin A−sin B)=0
By the sine rule, we have
asin A=bsin B=csin C=K(say)
⇒a=k sin A,b=k sin B and c=k sin C
∴LHS=a(sin B−sin C)+b(sin C−sin A)+c(sin A−sin B)
= k sin A(sin B−sin C)+k sin B(sin C−sin A)+k sin C(sin A−sin B)
=K[(sin A sin B−sin A sin C)+(sin B sin C−sin A sin B)+(sin A sin C−sin B sin C)]
(k×0)=0=RHS.