Áp dụng BĐT Cô-si:
\(\dfrac{a^2+1}{a}+\dfrac{a}{a^2+1}\ge2\sqrt{\dfrac{\left(a^2+1\right).a}{a.\left(a^2+1\right)}}=2\)
Vậy Pmin=2\(\Leftrightarrow\dfrac{a^2+1}{a}=\dfrac{a}{a^2+1}\)
\(\Rightarrow a^4+2a^2+1-a^2=0\)
\(\Leftrightarrow\left(a^2+1-a\right)\left(a^2+1+a\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}a^2-a+1=0\\a^2+a+1=0\end{matrix}\right.\)(vô nghiệm)
Vậy Pmin=2.
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