If [tex]$f(x) = 5x - 25$[/tex] and [tex]$g(x) = \frac{1}{5}x + 5$[/tex], which expression could be used to verify that [tex]g(x)[/tex] is the inverse of [tex]f(x)[/tex]?

A. [tex]\frac{1}{5}\left(\frac{1}{5}x + 5\right) + 5[/tex]
B. [tex]\frac{1}{5}(5x - 25) + 5[/tex]
C. [tex]\frac{1}{\left(\frac{1}{5}x + 5\right)}[/tex]
D. [tex]5\left(\frac{1}{5}x + 5\right) + 5[/tex]



Answer :

To determine which expression could be used to verify if [tex]\( g(x) = \frac{1}{5} x + 5 \)[/tex] is the inverse of [tex]\( f(x) = 5x - 25 \)[/tex], we need to follow these steps:

1. Understand the Definitions:
- The function [tex]\( f(x) = 5x - 25 \)[/tex].
- The function [tex]\( g(x) = \frac{1}{5} x + 5 \)[/tex].

2. Verify Inverse Relationship:
- For [tex]\( g(x) \)[/tex] to be the inverse of [tex]\( f(x) \)[/tex], we must have:
[tex]\[ g(f(x)) = x \quad \text{and} \quad f(g(x)) = x \][/tex]

3. Calculate [tex]\( g(f(x)) \)[/tex]:
[tex]\[ g(f(x)) = g(5x - 25) \][/tex]
Substitute [tex]\( 5x - 25 \)[/tex] into [tex]\( g(x) \)[/tex]:
[tex]\[ g(5x - 25) = \frac{1}{5} (5x - 25) + 5 = x - 5 + 5 = x \][/tex]
[tex]\( g(f(x)) = x \)[/tex], this part holds true.

4. Calculate [tex]\( f(g(x)) \)[/tex]:
[tex]\[ f(g(x)) = f\left( \frac{1}{5} x + 5 \right) \][/tex]
Substitute [tex]\( \frac{1}{5} x + 5 \)[/tex] into [tex]\( f(x) \)[/tex]:
[tex]\[ f\left(\frac{1}{5} x + 5\right) = 5\left(\frac{1}{5} x + 5\right) - 25 = x + 25 - 25 = x \][/tex]
[tex]\( f(g(x)) = x \)[/tex], this part also holds true.

5. List Possible Expressions:
Evaluate which of the given expressions simplifies to [tex]\( x \)[/tex]:
- [tex]\(\frac{1}{5}\left(\frac{1}{5} x + 5\right) + 5\)[/tex]
[tex]\[ \frac{1}{5}\left(\frac{1}{5} x + 5\right) + 5 = \frac{1}{25} x + 1 + 5 = \frac{1}{25} x + 6 \][/tex]
This does not simplify to [tex]\( x \)[/tex].

- [tex]\(\frac{1}{5}(5x - 25) + 5\)[/tex]
[tex]\[ \frac{1}{5}(5x - 25) + 5 = x - 5 + 5 = x \][/tex]
This simplifies to [tex]\( x \)[/tex].

- [tex]\(\frac{1}{\left(\frac{1}{5} x + 5\right)}\)[/tex]
[tex]\[ \frac{1}{\left(\frac{1}{5} x + 5\right)} = \text{This simplifies to} \frac{1}{5}x + 5 \text{ if this is the inverse} \][/tex]
This does not simplify to [tex]\( x \)[/tex].

- [tex]\( 5\left(\frac{1}{5} x + 5\right) + 5 \)[/tex]
[tex]\[ 5\left(\frac{1}{5} x + 5\right) + 5 = x + 25 + 5 = x + 30 \][/tex]
This does not simplify to [tex]\( x \)[/tex].

Based on this analysis, the second expression, [tex]\(\frac{1}{5}(5x - 25) + 5 \)[/tex], is the one that can be used to verify if [tex]\( g(x) \)[/tex] is the inverse of [tex]\( f(x) \)[/tex].

Therefore, the correct option is:
[tex]\[ \boxed{\frac{1}{5}(5x - 25) + 5} \][/tex]