阴影图形一般是不规则图形 .求解的基本方法是通过适当的变换把阴影部分的面积转化为规则图形的面积 ,或用代数方法求解 .常用的方法有如下几种 .一、旋转法直接计算阴影部分面积有困难可利用旋转的方法 ,形成新的图形 ,然后求解 .例 1　如图 1,在矩形ＡＢＣＤ中 ,长ＡＢ =ａ , Shadow graphics are generally irregular graphics. The basic method of solving is to transform the area of ​​the shadow part into an area of ​​a regular graph by appropriate transformation, or to use an algebraic method. There are several commonly used methods. First, the rotation method directly calculates the shadow Part of the area is difficult to use the rotation method to form a new figure, and then solve. Example 1 In Figure 1, in the rectangle ABCD, the length AB = a,