换元法可将原问题不断地转化,使问题简单化,易理解,有利于问题的解决.三角函数求值是考题中最常见的问题之一,在教学过程中发现不少学生在解此类问题时,看不出两个角之间的关系而一味正面突破,使解题过程复杂化导致耗时长甚至结果错误.本文通过换元法建立两个角与角t的直接明朗的关系,把已知和角(差角)的三角函数值转化为已知角t的三角函数值.如此一来,降低了此类问题的思维难度,简化了此类问题的 Replacing the original method can be constantly transformed, so that the problem is simple and easy to understand, is conducive to the solution of the problem.Calculation of trigonometric functions is one of the most common questions in the test, the process of teaching found that many students in the solution Class problems, we can not see that the relationship between the two corners blindly positive breakthrough, the problem-solving process is complicated and lead to long or even wrong results.This paper establishes a direct and clear relationship between two angles and angle t by the method of metamorphosis, Convert known and angular trigonometric values ​​into trigonometric values ​​of known angle t. As a result, the difficulty of thinking of such problems is reduced and the problem is simplified