First, calculate the distance from the center to the bottom, connect the center and point B, and make a vertical line from the center to BC. OA is on the same straight line with this vertical line, and the distance from the center to the bottom can be calculated as 3; There are two types of areas, one is (8*8)/2=32 square centimeters, and the other is (2*8)/2=8 square centimeters.