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求给定的三角函数式的极值,或按实际需要列出函数式求极值,是较常见而又较难把握的一类问题。我们给出五种常见解法。解题中,一是要注意分清字母变数与字母常数,不然,鱼龙混杂,思路不清;二是要注意几种方法的交错运用。(一)将含有多个(关于变量的)三角函数的函数式,经恒等变形,化为只含一个正弦(或余弦)的函数式,利用正弦(或余弦)的极值确定所求极值。
Finding the extremum of a given trigonometric function, or listing the extremum of a function based on actual needs, is a common and difficult problem to grasp. We give five common solutions. In the problem-solving problem, one must pay attention to clarifying the letter variables and letter constants. Otherwise, the pros and cons are mixed and the thinking is not clear; the second is to pay attention to the interleaving of several methods. (1) Convert a functional formula containing a number of trigonometric functions (of a variable) to an equation containing only one sine (or cosine) through an isomorphic transformation. Use the extremum of a sine (or cosine) to determine the value.