Question

Answer 1

a: \(a^2+b^2+c^2\ge ab+ac+bc\)

=>\(2a^2+2b^2+2c^2\ge2ab+2ac+2bc\)

=>\(2a^2+2b^2+2c^2-2ab-2ac-2bc\ge0\)

=>\(\left(a^2-2ab+b^2\right)+\left(a^2-2ac+c^2\right)+\left(b^2-2bc+c^2\right)\ge0\)

=>\(\left(a-b\right)^2+\left(a-c\right)^2+\left(b-c\right)^2\ge0\) (luôn đúng)