平行线是平面内两条直线的基本位置关系的一种,它的性质和位置关系是认识其他图形性质的基础,下面就同学们在学习平行线时经常出现的错误分析如下.一、概念不清例1如图1所示,下列各对角分别是什么角?(1)直线DE和BC被AB所截而得的∠ADE和∠B;被AC所截而得的∠C和∠DEC. The parallel line is one of the basic position relations of two straight lines in the plane. Its nature and position relationship is the basis for understanding other graphic properties. The following mistakes often occur when students study parallel lines are as follows: First, the concept is not Example 1 As shown in Figure 1, what angles are the following diagonals respectively? (1) ∠ADE and ∠B where the line DE and BC are truncated by AB; ∠C and ∠DEC truncated by the AC .