Remark
If you have the area of the sector, then what you need is the area of the triangle in order to find the area of the shaded area. Just subtract the two.
Area of the triangle
The right angle makes finding the base and height very easy since they are equal
Area_Triangle = 1/2 * b * h
b = 9
h = 9
Area = 1/2 * 9 * 9
Area = 1/2 * 81
Area = 40.5
Area of the Shaded Area
Area_shaded = area of the sector - area of the triangle.
Area_shaded = 20.25 * pi - 40.5
Area_shaded = 20.25(pi - 2) <<<< Answer
