$\begin{array}{l}1^{2}-1,2^{2}-1,3^{2}-1,4^{2}-1,5^{2}-1,6^{2}-1, \ldots A=4^{2}-1=15 \\ x^{2}-15 x+B=0 \\ 7+C=15 \Rightarrow C=8 \\ B=7 C=56 \\ \log _{7} 56=\log _{7} 8+7^{X} \\ 7^{X}=\log _{7}(56 / 8)=\log _{7} 7=1 \\ X=0\end{array}$
G9.1 Find $A$ from the sequence: $0,3,8, A, 24,35, \ldots$
G9.2 The roots of the equation $x^{2}-A x+B=0$ are 7 and $C$. Find $B$ and $C$.
G9.3 If $\log _{7} B=\log _{7} C+7^{X}$; find $X$.