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几何“确定”问题大致可分为定量、定形、定源三大类,定量问题即求符合已知条件的数量问题,它又分为定数值,定范围,定最值三类.定形问题即确定图形形状的问题,定源问题即追本溯源问题,根据原因和结果相互转化的辩证性质,就试题的表现形式而言,定源问题又可分为定条件,定结论两类。本文举例说明各类问题的思维规律和解答方法,仅供参考。一、定数值例1 在△ABC中,∠A是钝角,O是垂心,AO=BC,则cos(∠OBC+∠OCB)的值是( ) (93年全国竞赛题)
The “determined” problem of geometry can be roughly divided into three categories: quantitative, fixed, and fixed. The quantitative problem is the quantity problem that meets the known conditions. It is divided into three categories: fixed value, fixed range, and fixed maximum value. To determine the problem of the shape of the graph, the source problem is to trace the problem back to the source. According to the dialectical nature of the transformation of the cause and the result, the problem of the source of the problem can be divided into two categories: fixed conditions and final conclusions. This article illustrates the thinking patterns and solutions of various issues for reference only. First, the fixed value example 1 In △ ABC, ∠A is an obtuse angle, O is a vertical heart, AO = BC, then the value of cos (∠OBC + ∠OCB) is () (93 year national contest title)