|=0 ‌⇒b(b−c)−1(ab−c2)+a(a−c)=0 ‌⇒b2−bc−ab+c2+a2−ac=0 ‌⇒a2+b2+c2−ab−bc−ac=0 ‌⇒(a−b)2+(b−c)2+(c−a)2=0 ‌⇒‌‌a=b=c‌ i.e ‌A=B=C=60∘ [∵ Equilateral triangle has 3 sides of equal length and each angle is of measure 60∘ ]