在文 [1 ]中提出这样一个题目 :设 - 2π α β-π ,求 2α- β的范围 .图 1我们用图形法给出另一种解法 ,并很直观地给出一般情况下的结论 .建立如图 1的坐标系 ,易见α ,β的范围是图 1中的阴影部分 .设 2α- β =t则 β =2α -t表示直线 .由于α ,β的取值范围是图 1中的 In [1], we propose such a problem: Let -2π α β-π , find the range of 2α-β. Figure 1 We use the graphical method to give another solution and intuitively give conclusions under general conditions. To establish a coordinate system as shown in Figure 1, it is easy to see that the range of α and β is the shaded portion in Figure 1. Let 2α- β = t then β = 2α -t represents a straight line. Because α, β are in the range of Figure 1 middle