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lamlopbs


-Chứng minh :$\frac{a+b+c+d}{\sqrt[4]{abcd}}$ = $\frac{a+b}{2\sqrt[4]{abcd}}$ + $\frac{b+c}{\sqrt[4]{abcd}}$ + $\frac{c+d}{\sqrt[4]{abcd}}$ + $\frac{d+a}{\sqrt[4]{abcd}}$
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