Let $f ( x ) = \int _ { 1 } ^ { x ^ { 2 } } \frac { 4 - u } { \sin u + 2 } d u$

Essay

Let $f ( x ) = \int _ { 1 } ^ { x ^ { 2 } } \frac { 4 - u } { \sin u + 2 } d u$ Find the interval(s) on which $f ( x )$ is increasing.