a) \(a+\frac{1}{a}=3\)
\(\Leftrightarrow\)\(\left(a+\frac{1}{a}\right)^2=9\)
\(\Leftrightarrow\)\(a^2+2+\frac{1}{a^2}=9\)
\(\Leftrightarrow\)\(a^2+\frac{1}{a^2}=7\)
Ta có: \(\left(a+\frac{1}{a}\right)\left(a^2+\frac{1}{a^2}\right)=3.7\)
\(\Leftrightarrow\)\(a^3+\frac{1}{a}+a+\frac{1}{a^3}=21\)
\(\Leftrightarrow\)\(a^3+\frac{1}{a^3}=21-3=18\)
Ta lại có: \(\left(a^2+\frac{1}{a^2}\right)\left(a^3+\frac{1}{a^3}\right)=7.18\)
\(\Leftrightarrow\)\(a^5+\frac{1}{a}+a+\frac{1}{a^5}=126\)
\(\Leftrightarrow\)\(a^5+\frac{1}{a^5}=126-3=123\)