Sketch the Region Whose Area Is Given by the Definite $\int _ { 0 } ^ { 9 } \sqrt { 81 - t ^ { 2 } } d t$

Multiple Choice

Sketch the region whose area is given by the definite integral and then use a geometric formula to evaluate the integral. $\int _ { 0 } ^ { 9 } \sqrt { 81 - t ^ { 2 } } d t$

A) $\frac { 81 } { 4 } \pi$
B) $\frac { 81 } { 8 } \pi$
C) $\frac { 81 } { 2 } \pi$
D) $\frac { 81 } { 4 }$
E) $81 \pi$