Select the correct answer.

Which function defines [tex]\((g \cdot f)(x)\)[/tex] ?

[tex]\( f(x) = \log (5x) \)[/tex]
[tex]\( g(x) = 5x + 4 \)[/tex]

A. [tex]\((g \cdot f)(x) = 5x + 4 + \log (5x)\)[/tex]

B. [tex]\((g \cdot f)(x) = 5x \log (5x) + 4 \log (5x)\)[/tex]

C. [tex]\((g \cdot f)(x) = 5x \log (5x) + 4\)[/tex]

D. [tex]\((g \cdot f)(x) = 5x - 4 - \log (5x)\)[/tex]



Answer :

To determine the function [tex]\((g \cdot f)(x)\)[/tex], we need to find [tex]\(g(f(x))\)[/tex]. This means we will substitute [tex]\(f(x)\)[/tex] into [tex]\(g(x)\)[/tex].

We are given:
[tex]\[ f(x) = \log(5x) \][/tex]
[tex]\[ g(x) = 5x + 4 \][/tex]

Since we need [tex]\(g(f(x))\)[/tex], we substitute [tex]\(f(x)\)[/tex] into [tex]\(g(x)\)[/tex]:

1. Substitute [tex]\(f(x)\)[/tex] into [tex]\(g(x)\)[/tex]:
[tex]\[ g(f(x)) = g(\log(5x)) \][/tex]

2. Replace [tex]\(x\)[/tex] in [tex]\(g(x) = 5x + 4\)[/tex] with [tex]\(\log(5x)\)[/tex]:
[tex]\[ g(\log(5x)) = 5 \cdot \log(5x) + 4 \][/tex]

Therefore, the function [tex]\((g \cdot f)(x)\)[/tex] simplifies to:
[tex]\[ (g \cdot f)(x) = 5 \log(5x) + 4 \][/tex]

Now we need to match this expression with the given options:

A. [tex]\((g \cdot f)(x) = 5x + 4 + \log(5x)\)[/tex]

B. [tex]\((g \cdot f)(x) = 5x \log(5x) + 4 \log(5x)\)[/tex]

C. [tex]\((g \cdot f)(x) = 5x \log(5x) + 4\)[/tex]

D. [tex]\((g \cdot f)(x) = 5x - 4 - \log(5x)\)[/tex]

After comparing, the correct formula from our expression [tex]\(5 \log(5x) + 4\)[/tex] is:

C. [tex]\((g \cdot f)(x) = 5x \log(5x) + 4\)[/tex]

Thus, the correct answer is:

C. [tex]\((g \cdot f)(x) = 5x \log(5x) + 4\)[/tex]