[tex]\displaystyle\bf\\b_{9} =7\\\\b_{7} =252\\\\q=?\\\\\\\left \{ {{b_{9} =7} \atop {b_{7} =252}} \right. \\\\\\:\left \{ {{b_{1} \cdot q^{8} =7} \atop {b_{1}\cdot q^{6} =252 }} \right. \\---------\\q^{2} =\frac{7}{252} =\frac{1}{36} \\\\\\q_{1,2} =\pm \ \sqrt{\frac{1}{36} }=\pm \ \frac{1}{6} \\\\\\Otvet \ : \ q_{1} =-\frac{1}{6} \ \ ; \ \ q_{2}=\frac{1}{6}[/tex]