參考來源ppt:FAlin 應該是數學國手
\(\displaystyle (x+x+y)(1+\frac{y}{x}+1)\ge (\sqrt{x}+2\sqrt{y})^2\)
\(\displaystyle \Rightarrow \frac{2x+y}{(\sqrt{x}+2\sqrt{y})^2}\ge \frac{x}{2x+y} \)
\(\displaystyle \sum_{cyc}\frac{x(2x+y)}{z(\sqrt{x}+2\sqrt{y})^2}\ge \sum_{cyc} \frac{x^2}{yz+2xz}\ge \frac{(x+y+z)^2}{3xy+3yz+3zx}\ge 1 \)
倒數第二個柯西/權方和 最後一個
107.10.20版主補充出處
https://www.ptt.cc/bbs/Math/M.1539880910.A.B47.html
