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在三角问题中,注意观察式子的结构特征,做一些相应的代换,转化问题形式,可化生为熟,打开解题通道.本文分类列举介绍三角解题中的几种代换法.一、角的代换例1已知cos(α+π/4)=3/5,π/2≤α<3π/2,求cos(2α+π/4)的值.分析本例已知式中的角与所求式中的角差异大,难以沟通.若把α+π/4视为一个角,容易沟通已知
In the triangle problem, pay attention to observe the structural characteristics of the formula, do some corresponding substitution, conversion problems, can be born as cooked, open the problem-solving channel.This article introduces the classification of triangular solution in several substitution method. First, the angular substitution example 1 known cos (α + π / 4) = 3/5, π / 2 ≤ α <3π / 2, find cos (2α + π / 4) It is difficult to communicate if the angle in the formula is different from the angle in the formula, and if α + π / 4 is regarded as one corner, it is easy to communicate the known