神气猫
幼苗
共回答了14个问题采纳率：85.7% 举报
2/a^2+2/b^2+2/c^2+2/d^2
=(1/a^2+1/b^2)+(1/b^2+1/c^2)+(1/c^2+1/d^2)+(1/d^2+1/a^2)
>2√1/a^2b^2+2√1/b^2c^2+2√1/c^2d^2+2√1/d^2a^2
=2/|ab|+2/|bc|+2/|cd|+2/|da|
=2/ab+2/bc+2/cd+2/da
故
1/a^2+1/b^2+1/c^2+1/d^2>1/ab+1/bc+1/cd+1/da
证毕
1年前
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