二次函数 f(x)=ax~2+bx+c.(a≠0,x∈R)(1)是初等数学里最常见的函数,它的应用很广。本文将介绍二次函数的一个特性及其应用。 (一)二次函数的一个特性我们知道,二次函数 f(x)=ax~2+bx+c.(a≠0,x∈R)在任何一个闭区间[ξ,η]上连续,且在开区间(ξ,η)上可导(ξ∈R,η∈R,)。因此,微分中值定 The quadratic function f(x) = ax ~ 2 + bx + c. (a ≠ 0, x ∈ R) (1) is the most common function in elementary mathematics and its application is very wide. This article will introduce a feature of the quadratic function and its application. (A) A characteristic of the quadratic function We know that the quadratic function f(x) = ax~2+bx+c. (a ≠ 0, x ∈ R) is continuous over any closed interval [ξ, η]. And in the open interval (ξ, η) can lead (ξ∈R, η∈R,). Therefore, the differential median value