Editorial
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Editorial
- Use AM-GM inequality.
- You might find terms like $(x-y), (y-z)$ and $(z-x)$ while manipulating expressions. And you need to use $xy+yz+zx$ often in expansions.
Given real numbers $x, y, z$ where $xy+yz+zx \ge 0$. If $k(x^2+2yz)(y^2+2zx)(z^2+2xy) \le (x+y+z)^6$, then $k=?$.
[$k$ is an integer.]