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随着中考改革的不断深入,依纲据本的中考题都是经过妙构巧思编拟而成,很多题目的背景就是课本中的例题、习题或课本中某一概念、例题或思考题的重现.所以,中考复习要认真研究和挖掘课本.一、课本中例题的重现例1如图1,⊙O和⊙P外切于点A,EF是⊙和⊙P的公切线.E、F为切点.求证:EA⊥FA.这个结论也可变为:求证∠EAF+EAF=180°.(1)拖动直线EF,使其变化为⊙P的切线和⊙O的割线,如图2所示,此时,上述结论变为:
With the continuous deepening of the reform of the Chinese exam, the examination questions in accordance with the textbooks have been compiled through wonderful ideas. The background of many questions is the examples, exercises or textbooks in a textbook, examples, or questions. Reproduce. Therefore, the review of the examination requires careful study and excavation of the textbook. First, examples of the recurrence of examples in textbooks are shown in Figure 1. ⊙O and ⊙P are cut at point A, and EF is the common tangent of ⊙ and ⊙P. , F is the cut-point. Proof: EA ⊥ FA. This conclusion can also be changed to: 求 EAF + EAF = 180°. (1) Drag the line EF to change it to the tangent of ⊙P and the cut of ⊙O. As shown in Figure 2, the above conclusions are: