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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]


Sagot :

To find the inverse function of [tex]\( f(x) = -5x - 4 \)[/tex], we follow these steps:

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

2. Solve for [tex]\( x \)[/tex] in terms of [tex]\( y \)[/tex]:
- Add 4 to both sides:
[tex]\[ y + 4 = -5x \][/tex]
- Divide both sides by -5:
[tex]\[ x = -\frac{y + 4}{5} \][/tex]

Since dividing by -5 is the same as multiplying by [tex]\(-\frac{1}{5}\)[/tex], we get:
[tex]\[ x = -\frac{1}{5}(y + 4) \][/tex]

3. Rewrite the equation to express [tex]\( x \)[/tex] as a function of [tex]\( y \)[/tex]:
[tex]\[ x = -\frac{1}{5} y - \frac{4}{5} \][/tex]

4. Interchange [tex]\( x \)[/tex] and [tex]\( y \)[/tex] to get the inverse function:
[tex]\[ f^{-1}(x) = -\frac{1}{5} x - \frac{4}{5} \][/tex]

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

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