一、温固知新法将新旧知识有机的结合起来,使学生从旧知识的复习中自然获得新知识。例如在讲切割定理时,先复习相交弦定理内容及证明,即“圆”内两条相交弦被交点分成的两条线段长的积相等。然后移动两弦使其交点在圆外有三种情况。这样学生较易理解切割线定理、推论的数学表达式,在此基础上引导学生叙述定理内容,并总结圆幂定理的共同处是表示线段积相等。 First, Wen Gu knows that the new law combines organic knowledge with old and new knowledge so that students can naturally acquire new knowledge from the review of old knowledge. For example, in cutting the theorem, first review the contents of the intersecting string theorem and prove that the product of the two line segments divided by the intersection point in the circle is equal. Then move the two strings to make the intersection point outside the circle in three cases. In this way, students can easily understand the mathematical expressions of the cutting line theorem and inference, guide the students’ narrative theorems on the basis, and conclude that the common point of the circle power theorem is that the line segment products are equal.