6. Explain the following strange equation:
$$
\lg \left(16+\frac{16}{15}\right)=\lg 16+\lg \frac{16}{15}
$$
For positive numbers $a, b$, we have:
\[
\begin{aligned}
& \lg (a+b)=\lg a+\lg b \Leftrightarrow a+b=a b \\
\Leftrightarrow & a(b-1)=b \Leftrightarrow b>1, a=\frac{b}{b-1} .
\end{aligned}
\]