$$\left. \begin{array} { l } { ( 1 + \cos \frac { \pi } { 8 } ) ( 1 + \cos 3 \frac { \pi } { 8 } ) ( 1 + \cos 5 \pi ) ( 1 + \cos 7 \frac { \pi } { 8 } ) = \frac { 1 } { 8 } } \end{array} \right.$$
