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Posted by nhatanh2000 on 16-05-2016 - 15:51
cho a,b,c là các số dương thỏa mãn: a+b+c=3. Chứng minh rằng: $\frac{a}{2a+b}+\frac{b}{2b+c}+\frac{c}{2c+a}\leq 1$
Posted by nhatanh2000 on 24-03-2016 - 21:58
Chứng minh: $8+4tan\frac{\pi }{8}+2tan\frac{\pi }{16}+tan\frac{\pi }{32}=cot\frac{\pi }{32}$