12. Let the sequence $\frac{1}{2}, \frac{1}{4}, \frac{1}{8}, \cdots, \frac{1}{2^{n}}, \cdots$ have a subsequence, and this subsequence is an infinite series with a sum of $\frac{1}{7}$. The first term of this subsequence is $\qquad$ , and the common ratio is $\qquad$
12. $a_{1}=\frac{1}{8}, q=\frac{1}{8}$.