Which function is the inverse of [tex]f(x) = -5x - 4[/tex]?

A. [tex]f^{-1}(x) = -\frac{1}{5}x - \frac{4}{5}[/tex]
B. [tex]f^{-1}(x) = -\frac{1}{5}x + \frac{4}{5}[/tex]
C. [tex]f^{-1}(x) = -4x + 5[/tex]
D. [tex]f^{-1}(x) = 4x + 4[/tex]



Answer :

To determine the inverse of the function [tex]\( f(x) = -5x - 4 \)[/tex], we need to follow several steps to solve for the inverse function. Let's do this in a detailed, step-by-step manner.

1. Start with the original function [tex]\( y = -5x - 4 \)[/tex]:
[tex]\[ y = -5x - 4 \][/tex]

2. Switch [tex]\( x \)[/tex] and [tex]\( y \)[/tex] to begin solving for the inverse:
[tex]\[ x = -5y - 4 \][/tex]

3. Solve for [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex]:
- First, add 4 to both sides to begin isolating [tex]\( y \)[/tex]:
[tex]\[ x + 4 = -5y \][/tex]

- Next, divide both sides by [tex]\(-5\)[/tex]:
[tex]\[ y = \frac{-(x + 4)}{5} \][/tex]

4. Simplify the expression for [tex]\( y \)[/tex]:
[tex]\[ y = -\frac{x + 4}{5} \][/tex]
[tex]\[ y = -\frac{1}{5}x - \frac{4}{5} \][/tex]

So, the inverse function is:
[tex]\[ f^{-1}(x) = -\frac{1}{5}x - \frac{4}{5} \][/tex]

Now we need to match this result with one of the given choices:

1. [tex]\( f^{-1}(x) = -\frac{1}{5}x - \frac{4}{5} \)[/tex]
2. [tex]\( f^{-1}(x) = -\frac{1}{5}x + \frac{4}{5} \)[/tex]
3. [tex]\( f^{-1}(x) = -4x + 5 \)[/tex]
4. [tex]\( f^{-1}(x) = 4x + 4 \)[/tex]

Clearly, the correct option is:
[tex]\[ f^{-1}(x) = -\frac{1}{5}x - \frac{4}{5} \][/tex]

Therefore, the inverse function of [tex]\( f(x) = -5x - 4 \)[/tex] is [tex]\( -\frac{1}{5}x - \frac{4}{5} \)[/tex], which corresponds to:

[tex]\[ \boxed{1} \][/tex]