Evaluate $\iint _ { D } \frac { 1 } { \sqrt { x ^ { 2 } + y ^ { 2 } + 1 } } d A$

Essay

Evaluate $\iint _ { D } \frac { 1 } { \sqrt { x ^ { 2 } + y ^ { 2 } + 1 } } d A$ , where D is the region that lies between the circles $x ^ { 2 } + y ^ { 2 } = 1$ and $x ^ { 2 } + y ^ { 2 } = 9$ .