$$\frac{1}{(x+1)^2}+\frac{1}{(y+1)^2}+\frac{1}{(z+1)^2}+\frac{1}{(t+1)^2}\le 1$$
Chứng minh rằng: $x.y.z.t\ge 1$
Edited by 123123talackoka, 01-05-2012 - 13:54.
Edited by 123123talackoka, 01-05-2012 - 13:54.
Edited by Ispectorgadget, 13-05-2012 - 09:03.
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