论文部分内容阅读
ab±cd=ef型命题在中考中分量较大,一般与圆的条件给出,证明方法主要以三角形相似和有关圆的线段定理为推证依据。下面就将这类题证明方法总结如下。一、相似三角形结合相交弦定理例1 如图1,已知两圆内切于点P,大圆的弦AB切小圆于C,PC的延长线交大圆于点D,求证:(1)∠APD=∠BPD(2)PA·PB=PC+AC·CB(2000天津中考)。
The ab±cd=ef type proposition has a large weight in the middle examination, which is generally given by the condition of the circle. The proof method mainly uses the triangle similarity and the line segment theorem of the circle as the basis for the proof. The following is a summary of these problem-proving methods. First, the similar triangle combination of intersecting string theorem Example 1 As shown in Figure 1, known in the two circles in the cut point P, the big circle of the string AB cut small round in C, PC extended line of large circle in point D, verification: (1) ∠ APD=∠BPD(2) PA·PB=PC+AC·CB (2000 Tianjin Zhongkao).