If [tex][tex]$u(x) = -2x^2 + 3$[/tex][/tex] and [tex][tex]$v(x) = \frac{1}{x}$[/tex][/tex], what is the range of [tex][tex]$(u \cdot v)(x)$[/tex][/tex]?

A. [tex]\left(\frac{1}{3}, 0\right)[/tex]
B. [tex](3, \infty)[/tex]
C. [tex](-\infty, 3)[/tex]
D. [tex](-\infty, +\infty)[/tex]



Answer :

To determine the range of the function [tex]\((u \cdot v)(x)\)[/tex], where [tex]\(u(x) = -2x^2 + 3\)[/tex] and [tex]\(v(x) = \frac{1}{x}\)[/tex], we need to examine the behavior of their product [tex]\((u \cdot v)(x)\)[/tex].

First, let's denote the product function as [tex]\(f(x)\)[/tex]:
[tex]\[ f(x) = u(x) \cdot v(x) = (-2x^2 + 3) \cdot \frac{1}{x} \][/tex]

Simplifying [tex]\(f(x)\)[/tex], we get:
[tex]\[ f(x) = -2x + \frac{3}{x} \][/tex]

To understand the range of [tex]\(f(x)\)[/tex], let's analyze the expression [tex]\(-2x + \frac{3}{x}\)[/tex].

The behavior of the function as [tex]\(x\)[/tex] varies:
1. As [tex]\(x\)[/tex] approaches 0 from the positive side ([tex]\(x \to 0^+\)[/tex]):
[tex]\[ -2x \to 0 \quad \text{and} \quad \frac{3}{x} \to +\infty \][/tex]
Therefore, [tex]\(f(x) \to +\infty\)[/tex].

2. As [tex]\(x\)[/tex] approaches 0 from the negative side ([tex]\(x \to 0^-\)[/tex]):
[tex]\[ -2x \to 0 \quad \text{and} \quad \frac{3}{x} \to -\infty \][/tex]
Therefore, [tex]\(f(x) \to -\infty\)[/tex].

3. As [tex]\(x\)[/tex] approaches [tex]\(\infty\)[/tex]:
[tex]\[ -2x \to -\infty \quad \text{and} \quad \frac{3}{x} \to 0 \][/tex]
Therefore, [tex]\(f(x) \to -\infty\)[/tex].

4. As [tex]\(x\)[/tex] approaches [tex]\(-\infty\)[/tex]:
[tex]\[ -2x \to +\infty \quad \text{and} \quad \frac{3}{x} \to 0 \][/tex]
Therefore, [tex]\(f(x) \to +\infty\)[/tex].

Given this analysis, we can see that as [tex]\(x\)[/tex] varies over the real numbers (except zero), the function [tex]\(f(x) = -2x + \frac{3}{x}\)[/tex] takes on all real values.

Thus, the range of the function [tex]\((u \cdot v)(x)\)[/tex] is:
[tex]\[ (-\infty, +\infty) \][/tex]

So, the correct answer is:
[tex]\[ \boxed{(-\infty, +\infty)} \][/tex]