教材理解与教学设计的指导思想:本节课是在学生已经学习了特殊四边形及三角形、梯形的中位线相关知识后的复习课。三角形和梯形的中位线,是初中几何中一个非常重要的知识点。其定理所显示的特点是既包含了线段间的数量关系,又包含了直线间的位置关系,因此为证明线段间的倍分关系及两直线的平行关系提供了依据。本节课是对三角形和梯形中位线知识的进一步深化和运用。教学设计的想法是解决三种情况的问 Teaching material understanding and teaching design guidelines: This lesson is after the students have learned special quadrilateral and triangular, trapezoidal midline related knowledge of the review class. The median line of the triangle and trapezoid is a very important point of knowledge in junior high school geometry. The theorem shows that the characteristic includes not only the quantitative relationship between the line segments but also the position relationship between the straight lines. Therefore, it provides the basis for the proof of the multiple relations and the parallel relationship between two lines. This lesson is to further deepen and apply the knowledge of the bit lines in the triangle and trapezoid. The idea of ​​instructional design is to solve three situations