Tìm max min

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20071006

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E

eye_smile


Từ gt \Rightarrow $2ab+2bc+2ca={a^2}+{b^2}+{c^2}$
\Rightarrow $P=\dfrac{2{a^2}+{b^2}+{c^2}}{ab+bc+ca}=2+\dfrac{{a^2}}{ab+bc+ca}$
Do $2ab+2bc+2ca={a^2}+{b^2}+{c^2}$ \Rightarrow $ab+bc+ca$ dương
\Rightarrow $\dfrac{{a^2}}{ab+bc+ca}$ \geq 0
\Rightarrow $P_{min}=2$ tại $a=0$; b=c
 
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