Question 78
Find all positive real numbers $c$ such that
$$
\frac{x^3y + y^3z + z^3x}{x + y + z} + \frac{4c}{xyz} \geq 2c + 2
$$
for all positive real numbers $x, y, z$.
$$
\frac{x^3y + y^3z + z^3x}{x + y + z} + \frac{4c}{xyz} \geq 2c + 2
$$
for all positive real numbers $x, y, z$.