LHS=a2+b2+c2−ab−bc−ac=12[2a2+2b2+2c2−2ab−2bc−2ac]=12[a2−2ab+b2+b2−2bc+c2+c2−2ac+a2]=12[(a−b)2+(b−c)2+(c−a)2]
If a + b + c = 0, then prove the following
(a) (b + c) (b − c) + a(a + 2b) = 0
(b) a(a2 − bc) + b(b2 − ca) + c(c2 − ab) = 0
(c) a(b2 + c2) + b(c2 + a2) + c(a2 + b2) = −3abc
(d)