\[\boxed{\text{709\ (709).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[b_{n} = b_{1} \cdot q^{n - 1},\]
\[b_{m} = b_{1} \cdot q^{m - 1},\]
\[b_{1} = \frac{b_{m}}{q^{m - 1}},\]
\[b_{n} = \frac{b_{m}}{q^{m - 1}} \cdot q^{n - 1} =\]
\[= b_{m} \cdot q^{n - 1 - m + 1} = b_{m} \cdot q^{n - m}.\]