The integral $\int _ { 1 / 4 } ^ { 3 / 4 } \cos \left( 2 \cot ^ { - 1 } \sqrt { \frac { 1 - x } { 1 + x } } \right) d x$ is equal to\\ (1) $1 / 2$\\ (2) $- 1 / 2$\\ (3) $- 1 / 4$\\ (4) $1 / 4$