왜 2ab+2bc+2ac=-(a&\#178;+b²+c²)=-100 왜 a&\#178;+b²+c²+2ab+2b+2bc=0

왜 2ab+2bc+2ac=-(a&\#178;+b²+c²)=-100 왜 a&\#178;+b²+c²+2ab+2b+2bc=0

(a+b+c)²=[(a+b)+c]²=(a+b)²+2(a+b)c+c²=a²+2ab+b²+2ac+2bc+c²=a²+b²+c²+2ab+2bc+2ac 그리고 이 항 은 2ab+2bc+2ac=-(a&\#178;+b²+c²)