Use a Sign Chart to Determine the Intervals on Which $f ( x ) = \frac { 1 } { x ^ { 2 } + 4 }$

Essay

Use a sign chart to determine the intervals on which $f ( x ) = \frac { 1 } { x ^ { 2 } + 4 }$ is concave up and concave down, and identify the locations of any inflection points.