2. Simplify $\left(\log _{3} 4+\log _{2} 9\right)^{2}-\left(\log _{3} 4-\log _{2} 9\right)^{2}$ $=$ $\qquad$
2.16.
$$
\begin{array}{l}
(\log 4+\log 9)^{2}-(\log 4-\log 9)^{2} \\
=4 \log 4 \cdot \log 9=4 \times \frac{\log 4}{\log 3} \times \frac{\log 9}{\log 2} \\
=4 \times \frac{2 \log 2}{\log 3} \times \frac{2 \log 3}{\log 2}=16 .
\end{array}
$$