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I come across to a simple-looking ineqality. But I cann't prove it for quite a long time. Could any body give a hint? Thanks a lot!

[tex]

2[(n-1) \sum_{j=1}^n r_j^2 -(n-2) r_n^2] \geq (\sum_{j=1}^n r_j)^2

[/tex]

where [tex]n\geq 2, \forall r_j \geq 0, j=1,2,\cdots,n[/tex].

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# Help on simple-looking ineqality

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