$$\text { Find the interval on which the curve } F ( x ) = \int _ { 0 } ^ { x } \frac { d t } { 11 + 11 t } \text { is concave downward. }$$

$$\text { Find the interval on which the curve } F ( x ) = \int _ { 0 } ^ { x } \frac { d t } { 11 + 11 t } \text { is concave downward. }$$