Finding the shadow area is common sense in primary school mathematics, and it is also a difficult problem for some students. But as long as we master the methods and practice hard, we can solve these problems. Here are a few examples for everyone to see.

0 1 cut-and-complement method and segmentation method are used in geometry problems. Cut-and-fill method is to cut off the graphics and move the cut-off parts to other positions, so that the questions are easy to answer; Segmentation is to divide the figure equally, but not move, so that the problem can be solved easily.

First of all, the first question: if you know the side length of the square OCDE, you can know the radius of the sector. We can add the area of rectangular ACDF to the area of BDE, where the long side of the rectangle CD= 1 and the short side AC = OA-oc; Then the BDE area is equal to the sector area minus half the square area.

In the second question, we can fill the upper fan-shaped shadow into the lower blank, so that the total shadow area is exactly the area of triangle ACD, and because the angle ADC is right angle, the shadow area can be calculated quickly.

In this problem, we can subtract the areas of three sectors from the area of a triangle. The triangle is a regular triangle, so the angle of each sector is 60? Three sectors add up to the area of half a circle, which is also easy to calculate.

The shaded part of this problem is three sectors with unknown angles, but the radii of the three sectors are all the same, because the sum of the internal angles of the triangle is 180? So the shadow area is the area of a semicircle with a fan-shaped radius.

The shadow part of this problem consists of a sector and an irregular figure. Cut the sector in the upper right corner into the corresponding blank on the left, and the shadow becomes a triangle. If the side length of a triangle is known, the shadow area can be calculated.