Cho a,b,c > 0 chứng minh rằng
$\frac{a}{a+b}+\frac{b}{b+c}+\frac{c}{c+a}<2$
Cho a,b,c > 0 CMR $\frac{a}{a+b}+\frac{b}{b+c}+\frac{c}{c+a}<2$
Started By cold_noodles97, 29-03-2012 - 11:35
#1
Posted 29-03-2012 - 11:35
#2
Posted 29-03-2012 - 12:30
Cho a,b,c > 0 chứng minh rằng
$\frac{a}{a+b}+\frac{b}{b+c}+\frac{c}{c+a}<2$
Ta có: $$a < a + b \Rightarrow \frac{a}{{a + b}} < \frac{{a + c}}{{a + b + c}}$$
Tương tự: $$\frac{b}{{b + c}} > \frac{{a + b}}{{a + b + c}};\,\,\frac{c}{{c + a}} < \frac{{b + c}}{{a + b + c}}$$
Cộng các bất đẳng thức trên vế theo vế, ta được:
$$\frac{a}{{a + b}} + \frac{b}{{b + c}} + \frac{c}{{c + a}} < \frac{{2\left( {a + b + c} \right)}}{{a + b + c}} = 2$$
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