在求函数 ｙ =Ａ·ｓｉｎ(ωｘ +φ)及 ｙ =Ａ·ｃｏｓ(ωｘ +φ)的单调区间时 ,学生往往容易出错 ,特别是在ω 0的情况下 ,尤为突出 .本文介绍一种既保险又快捷的求法 ,解法分三步 .第一步 :求出函数的最小正周期Ｔ =2π|ω|;第二步 :寻找一个ｘ0 ,使ｘ =ｘ0 时 ,ｙ值最大 ;? In finding monotonic intervals of the functions y = A · sin (ω x + φ) and y = A · cos (ω x + φ), students are often prone to errors, especially in the case of ω 0. This article describes a Safe and fast method of seeking, the solution is divided into three steps. The first step: find the minimum positive cycle of the function T = 2π | ω |; second step: find a x0, so that when x = x0, y value is the largest;