Đáp án:
$\begin{array}{l}
a)\frac{{{3^{12}} - 1}}{{{3^{14}} - 1}} < 1\\
\Rightarrow \frac{{{3^{12}} - 1}}{{{3^{14}} - 1}} > \frac{{{3^{12}} - 1 - 8}}{{{3^{14}} - 1 - 8}}\\
\Rightarrow \frac{{{3^{12}} - 1}}{{{3^{14}} - 1}} > \frac{{{3^{12}} - {3^2}}}{{{3^{14}} - {3^2}}}\\
\Rightarrow \frac{{{3^{12}} - 1}}{{{3^{14}} - 1}} > \frac{{{3^{10}} - 1}}{{{3^{12}} - 1}}\\
b)\frac{{{7^{22}} - 1}}{{1 - {7^{22}}}} = - 1\\
\frac{{{7^{20}} - 1}}{{1 - {7^{22}}}} = - \frac{{{7^{20}} - 1}}{{{7^{22}} - 1}}\\
Do:\frac{{{7^{20}} - 1}}{{{7^{22}} - 1}} < 1\\
\Rightarrow - \frac{{{7^{20}} - 1}}{{{7^{22}} - 1}} > - 1\\
\Rightarrow \frac{{{7^{20}} - 1}}{{1 - {7^{22}}}} > \frac{{{7^{22}} - 1}}{{1 - {7^{22}}}}
\end{array}$
