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If [tex]\( f(x) = x + 7 \)[/tex] and [tex]\( g(x) = \frac{1}{x-13} \)[/tex], what is the domain of [tex]\( (f \circ g)(x) \)[/tex]?

A. [tex]\( \{ x \mid x \neq 6 \} \)[/tex]
B. [tex]\( \{ x \mid x \neq -6 \} \)[/tex]
C. [tex]\( \{ x \mid x \neq -13 \} \)[/tex]
D. [tex]\( \{ x \mid x \neq 13 \} \)[/tex]

Sagot :

To determine the domain of [tex]\((f \circ g)(x)\)[/tex], we need to understand the individual domains of the functions [tex]\(f(x)\)[/tex] and [tex]\(g(x)\)[/tex] and then find where the composition is defined.

1. First, consider the function [tex]\(g(x) = \frac{1}{x - 13}\)[/tex].
- The domain of [tex]\(g(x)\)[/tex] is all real numbers except where the denominator is zero.
- So, [tex]\(x - 13 \neq 0\)[/tex] which means [tex]\(x \neq 13\)[/tex].
- Therefore, the domain of [tex]\(g(x)\)[/tex] is [tex]\(\{x \mid x \neq 13\}\)[/tex].

2. Next, consider the function [tex]\(f(x) = x + 7\)[/tex].
- The function [tex]\(f(x)\)[/tex] is defined for all real numbers.
- Therefore, the domain of [tex]\(f(x)\)[/tex] is all real numbers, [tex]\(\mathbb{R}\)[/tex].

3. Now, we consider the composition [tex]\((f \circ g)(x)\)[/tex], which is [tex]\(f(g(x))\)[/tex].
- The composition [tex]\((f \circ g)(x)\)[/tex] is defined wherever [tex]\(g(x)\)[/tex] is defined and [tex]\(g(x)\)[/tex] produces a result within the domain of [tex]\(f\)[/tex].

Since the domain of [tex]\(g(x)\)[/tex] is [tex]\(\{x \mid x \neq 13\}\)[/tex], and [tex]\(f\)[/tex] is defined for all real numbers, the only restriction for the composition [tex]\((f \circ g)(x)\)[/tex] comes from the restriction on [tex]\(g(x)\)[/tex].

Thus, the domain of [tex]\((f \circ g)(x)\)[/tex] is [tex]\(\{x \mid x \neq 13\}\)[/tex].

The correct answer is:
[tex]\(\{x \mid x \neq 13\}\)[/tex]