数列极限中有著名的“两边夹”定理: 若an≤bn≤cn,且liman=limcn=A,则limbn=A. 由于数列是一种特殊的函数,上述定理可以移植到函数当中: 如果函数f(x)在区间D上满足g(x)≤f(x)≤h(x),且g(x)≤h(x)在区间D上恒成立.若存在x0∈D使g(x0)=h(x0)=A,则f(x0)=A. 不妨将这一命题称为函数中的“两边夹定理”,这个十分简明的结论,在高中数学中有着非常重要的作用,但在具体应用中要注意“恒”成立这一条 There are the well-known “two-sided folder” theorem in the limit of the series: if an ≤ bn ≤ cn, and liman = limcn = A, then limbn = A. Since the series is a special function, the above theorems can be transplanted into the function: If the function f(x) satisfies g(x)≤f(x)≤h(x) in interval D, and g(x)≤h(x) is constant in interval D. If x0∈D is present, g(x0) ) = h (x0) = A, then f (x0) = A. This proposition may be called the “two-sided folder theorem” in the function, this very concise conclusion, has a very important role in high school mathematics, but In the specific application, we must pay attention to the establishment of “constant”