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Mathematics · 术语表

什么是 Function, domain, curve?

又称: function · domain

Definition 11.1 High School Mathematics · 第 11 章 — Functions and Variations

A function ff assigns to each number xx of a set D⊆RD \subseteq \R (its domain) exactly one number f(x)f(x). Its curve (or graph) is the set of points (x,f(x))\bigl(x, f(x)\bigr) for x∈Dx \in D.

示例

Example 11.10

Study f(x)=x2+1f(x) = \sqrt{x^2 + 1} on R\R. The inner function u(x)=x2+1u(x) = x^2 + 1 is positive, decreasing on (−∞, 0]\intoc{-\infty}{0} and increasing on [0, +∞)\intco{0}{+\infty} (a shifted square). By point 3, ff has the same variations: decreasing then increasing, with minimum f(0)=1f(0) = 1.

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