许多数学问题 ,往往只是一字之差 ,但审题不严、理解有误 ,则会导致解题错误 ,可谓“差之毫厘 ,谬之千里” .不等式的“能”成立、“恒”成立与“恰”成立问题便是一例 .例 1　已知 f(x)是定义在 (-∞ ,4 ]上的减函数 ,若 f(m -sinx)≤ f 1+2m - 74 +cos2 x对一切实数x恒成立 , Many mathematics problems are often only one word difference, but if they are not well-understood or misunderstood, they will lead to mistakes in solving problems. It can be said that “the difference is insignificant, and the difference is a thousand miles.” The inequality “energy” is established, and “constant” is established. An example of the “right” formation problem is an example. Example 1 It is known that f(x) is a decreasing function defined on (-∞, 4 ) if f(m -sinx) ≤ f 1+2m - 74 +cos2 x The effective number x is established,