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Comparing a Function and Its Inverse

Consider the function
[tex]\[ f(x)=\frac{3}{4} x+12 \][/tex]

What is the [tex]$y$[/tex]-intercept of [tex]$f^{-1}(x)$[/tex]?

A. \(-16\)
B. \(-\frac{3}{4}\)
C. [tex]\(\frac{4}{3}\)[/tex]

Sagot :

To find the y-intercept of the inverse function \( f^{-1}(x) \), we need to follow several steps in transforming and solving the given function. Here’s the detailed process:

1. Given Function:
The function is given as:
[tex]\[ f(x) = \frac{3}{4} x + 12 \][/tex]

2. Express as \( y = f(x) \):
Rewrite the function with \( y \):
[tex]\[ y = \frac{3}{4} x + 12 \][/tex]

3. Swap \( x \) and \( y \):
To find the inverse function, switch \( x \) and \( y \):
[tex]\[ x = \frac{3}{4} y + 12 \][/tex]

4. Solve for \( y \):
Isolate \( y \) to express the inverse function:
- Subtract 12 from both sides:
[tex]\[ x - 12 = \frac{3}{4} y \][/tex]

- Multiply both sides by \( \frac{4}{3} \):
[tex]\[ y = \frac{4}{3} (x - 12) \][/tex]

So, the inverse function is:
[tex]\[ f^{-1}(x) = \frac{4}{3} (x - 12) \][/tex]

5. Find the \( y \)-intercept of the inverse function:
The y-intercept occurs when \( x = 0 \):

- Substitute \( x = 0 \) into the inverse function:
[tex]\[ f^{-1}(0) = \frac{4}{3} (0 - 12) \][/tex]
[tex]\[ f^{-1}(0) = \frac{4}{3} \cdot (-12) \][/tex]
[tex]\[ f^{-1}(0) = -16 \][/tex]

The y-intercept of the inverse function \( f^{-1}(x) \) is \( -16 \). Thus, the correct answer is:

[tex]\[ \boxed{-16} \][/tex]