关于有约束条件的三角函数取值范围问题是一类极易产生错解的问题,原因是对于正余弦函数能否取到上确界1和下确界-1没有给予特别的关注,防止出错的有效措施是要增加检验的环节,即能否找到待求值式取到特殊值时对应的自变量的值(找到即可,不一定要找到全体的值)是解题成败与对错的关键. The question of the range of trigonometric functions with constraints is a type of problem that can easily cause misinterpretation because no particular attention is given to whether the positive cosine function has the upper bound 1 and the lower bound -1, The effective measure is to increase the inspection link, that is, whether the value of the independent variable can be found when the value of the special value is to be found (find, not necessarily find the value of all) is the problem of success or failure The essential.