Figure 1 and Figure 2 form a sector figure to find the area, and Figure 2, Figure 3 and Figure 4 form a semicircle figure to find the area. Adding the sector area to the semicircle area is equivalent to Figure 1 plus Figure 2 plus Figure 2 plus Figure 3 plus Figure 4 (that is, Figure 1+2+3+4) to find the area of the shaded part. Then the area of the sector plus the semicircle will add the area of figure 2 and figure 3 of figure 1. As shown in the figure, figure 2 of figure 1 forms a triangle, and then a triangle is subtracted from a sector plus a semicircle, which is the figure in the shadow area (1+2+3+4- 1-2