turkey-yks 2012 Q33

turkey-yks · Other · lys1-math Sequences and Series Limit Evaluation Involving Sequences
The sequence $\left( a _ { n } \right)$
$$a _ { n } = \begin{cases} 2 ^ { n } + 1 , & n \equiv 0 ( \bmod 2 ) \\ 2 ^ { n } - 1 , & n \equiv 1 ( \bmod 2 ) \end{cases}$$
is defined in the form. Accordingly, what is the value of the expression $\frac { a _ { 9 } - a _ { 7 } } { a _ { 8 } - 4 \cdot a _ { 6 } }$?
A) $-2 ^ { 8 }$
B) $-2 ^ { 7 }$
C) $-2 ^ { 6 }$
D) $-2 ^ { 5 }$
E) $-2 ^ { 4 }$
The sequence $\left( a _ { n } \right)$

$$a _ { n } = \begin{cases} 2 ^ { n } + 1 , & n \equiv 0 ( \bmod 2 ) \\ 2 ^ { n } - 1 , & n \equiv 1 ( \bmod 2 ) \end{cases}$$

is defined in the form. Accordingly, what is the value of the expression $\frac { a _ { 9 } - a _ { 7 } } { a _ { 8 } - 4 \cdot a _ { 6 } }$?

A) $-2 ^ { 8 }$\\
B) $-2 ^ { 7 }$\\
C) $-2 ^ { 6 }$\\
D) $-2 ^ { 5 }$\\
E) $-2 ^ { 4 }$