Let a, B, C be real numbers, and prove: A & sup2; B & sup2; + B & sup2; C & sup2; + A & sup2; C & sup2; ≥ ABC (a + B + C)

Let a, B, C be real numbers, and prove: A & sup2; B & sup2; + B & sup2; C & sup2; + A & sup2; C & sup2; ≥ ABC (a + B + C)

It is proved that: ∵ A & sup2; B & sup2; + B & sup2; C & sup2; ≥ 2Ab & sup2; C,
b²c²+c²a²≥2abc²,
c²a²+a²b²≥2a²bc,
The above three inequalities add up to a & sup2; B & sup2; + B & sup2; C & sup2; + C & sup2; a & sup2; ≥ ABC (a + B + C)