9. As shown in the figure, the diagonal $B D$ of square $A B C D$ is 20 cm long, and $B D F E$ is a rectangle. Then, the area of pentagon $A B E F D$ is
$\qquad$ square centimeters.
【Analysis】300 square centimeters
Connecting lines as shown in the figure can divide the shape into 6 equal parts, where the area of any one part is $10 \times 10 \div 2=50$ square centimeters; therefore, the area of pentagon $A B E F D$ is $50 \times 6=300$ square centimeters.