12.5pi-25
由直角三角形三边关系可得OA^2 = AB^2 / 2 = 50
S扇形OAB = pi * OA^2 / 4 = 12.5pi
S三角形OAB = 1/2 * OA^2 = 25
S阴影 = S扇形OAB - S三角形OAB = 12.5*pi - 25
12.5pi-25
由直角三角形三边关系可得OA^2 = AB^2 / 2 = 50
S扇形OAB = pi * OA^2 / 4 = 12.5pi
S三角形OAB = 1/2 * OA^2 = 25
S阴影 = S扇形OAB - S三角形OAB = 12.5*pi - 25