Rút gọn biểu thức: (a+b+c)^2 +(a-b-c)^2 +(b-c-a)^2 +(c-a-b)^2

a+b+c2+a−b−c2+b−c−a2+c−a−b2

=a2+b2+c2+2ab+2ac+2bc+a2+b2+c2−2ab−2ac+2bc+a2+b2+c2−2ab+2ac−2bc

=4a2+b2+c2