If [tex]\( f(x)=\frac{x-3}{x} \)[/tex] and [tex]\( g(x)=5x-4 \)[/tex], what is the domain of [tex]\((f \circ g)(x)\)[/tex]?

A. [tex]\( \{x \mid x \neq 0\} \)[/tex]

B. [tex]\( \left\{ x \left\lvert\, x\ \textless \ \frac{1}{3}\right. \right\} \)[/tex]

C. [tex]\( \left\{ x \left\lvert\, x\ \textless \ \frac{4}{5}\right. \right\} \)[/tex]

D. [tex]\( \{x \mid x \neq 3\} \)[/tex]



Answer :

To find the domain of [tex]\((f \circ g)(x)\)[/tex], which represents [tex]\(f(g(x))\)[/tex], let's follow these steps:

1. Understand the domain of [tex]\(f(x)\)[/tex]:
The function [tex]\(f(x) = \frac{x-3}{x}\)[/tex] has a restriction due to the denominator: [tex]\(x \neq 0\)[/tex]. Hence, the domain of [tex]\(f(x)\)[/tex] is all real numbers except [tex]\(x = 0\)[/tex].

2. Apply [tex]\(g(x)\)[/tex]:
The function [tex]\(g(x) = 5x - 4\)[/tex] is a linear function and is defined for all real numbers. There are no restrictions on its domain.

3. Determine the domain of [tex]\(f(g(x))\)[/tex]:
We need to find when the argument [tex]\(g(x)\)[/tex] makes [tex]\(f(g(x))\)[/tex] undefined. This occurs if:

[tex]\[ g(x) = 0 \][/tex]

1. Solve for [tex]\(x\)[/tex]:

[tex]\[ 5x - 4 = 0 \][/tex]

[tex]\[ 5x = 4 \][/tex]

[tex]\[ x = \frac{4}{5} \][/tex]

Therefore, [tex]\(x = \frac{4}{5}\)[/tex] is the value that makes [tex]\(g(x)\)[/tex] equal to zero, causing [tex]\(f(g(x))\)[/tex] to be undefined.

4. State the domain of [tex]\((f \circ g)(x)\)[/tex]:
The domain of [tex]\((f \circ g)(x)\)[/tex] includes all real numbers except the value where [tex]\(g(x)\)[/tex] turns the argument of [tex]\(f\)[/tex] into 0. Hence, we exclude [tex]\(x = \frac{4}{5}\)[/tex].

By analyzing the exclusions, the domain of [tex]\((f \circ g)(x)\)[/tex] is:

[tex]\[ \{x \mid x \neq \frac{4}{5}\} \][/tex]

Therefore, the correct option is:

[tex]\(\left\{x \mid x \neq \frac{4}{5}\right\}\)[/tex].