a2 sin (B−C)sin A+b2 sin (C−A)sin B+c2 sin (A−B)sin C=0
a2 sin (B−C)sin A+b2 sin (C−A)sin B+c2 sin (A−B)sin C=0asin A=bsin B=csin C=kLHSa2 sin (B−C)sin A+b2 sin (C−A)sin B+c2 sin (A−B)sin C=ak sin (B−C)+bk sin (C−A)+ck sin (A−B)=sin A sin (B−C)+sin B sin (C−A)+sin C sin (A−B)=sin (π−(B+C))sin (B−C)+sin (π−(C+A)) sin (C−A)+sin (π−(A+B))sin (A−B)=sin (B+C) sin (B−C)+sin (C+A) sin (C−A)+sin (A+B)sin (A−B)=sin2 B−sin2 C+sin2 C−sin2 A+sin2 A−sin2 B=0=RHS