Ta có:
\(\frac{a+1}{a-1}+\frac{a-1}{a+1}=\frac{a-1+2}{a-1}+\frac{a+1-2}{a+1}=1+\frac{2}{a-1}+1-\frac{2}{a+1}=2+\left(\frac{2}{a-1}-\frac{2}{a+1}\right)\)
Ta lại có:
\(a-1< a+1\Rightarrow\frac{2}{a-1}>\frac{2}{a+1}\)
\(\Rightarrow\frac{2}{a-1}-\frac{2}{a+1}>0\)
\(\Rightarrow2+\frac{2}{a-1}-\frac{2}{a+1}>2\)
\(\Rightarrow\frac{a+1}{a-1}+\frac{a-1}{a+1}>2\left(đpcm\right)\)