Cho $n$ số thực $x_1,x_2,...,x_n$.Chứng minh rằng:
$\frac{x_1}{1+x_1^2}+\frac{x_2}{1+x_1^2+x_2^2}+...+\frac{x_n}{1+x_1^2+x_2^2+...+x_n^2}\leqslant \sqrt{n}$
$\frac{x_1}{1+x_1^2}+\frac{x_2}{1+x_1^2+x_2^2}+...+\frac{x_n}{1+x_1^2+x_2^2+...+x_n^2}\leqslant \sqrt{n}$
Started By Minhnguyenthe333, 21-05-2016 - 10:56
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