Question 81
Find the greatest real number $M$ satisfying
$$
a^3 + b^3 + c^3 - 3abc \geq M(ab^2 + bc^2 + ca^2 - 3abc)
$$
for all positive real numbers $a, b, c$.
$$
a^3 + b^3 + c^3 - 3abc \geq M(ab^2 + bc^2 + ca^2 - 3abc)
$$
for all positive real numbers $a, b, c$.