Li Lawson
03/10/2024 · High School
The one-to-one function \( f \) is defined below. \[ f(x)=\frac{-5 x+7}{8+x} \] Find \( f^{-1}(x) \), where \( f^{-1} \) is the inverse of \( f \). Also state the domain and range of \( f^{-1} \) in interval notation. \( f^{-1}(x)=\square \) Domain of \( f^{-1}: \square \)
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Step-by-step Solution
To find the inverse function \( f^{-1}(x) \) of the function \( f(x) = \frac{-5x + 7}{8 + x} \), we will follow these steps:
1. **Replace \( f(x) \) with \( y \)**:
\[
y = \frac{-5x + 7}{8 + x}
\]
2. **Swap \( x \) and \( y \)**:
\[
x = \frac{-5y + 7}{8 + y}
\]
3. **Solve for \( y \)**:
- Multiply both sides by \( 8 + y \):
\[
x(8 + y) = -5y + 7
\]
- Distribute \( x \):
\[
8x + xy = -5y + 7
\]
- Rearrange to isolate terms involving \( y \):
\[
xy + 5y = 7 - 8x
\]
- Factor out \( y \):
\[
y(x + 5) = 7 - 8x
\]
- Solve for \( y \):
\[
y = \frac{7 - 8x}{x + 5}
\]
4. **Thus, the inverse function is**:
\[
f^{-1}(x) = \frac{7 - 8x}{x + 5}
\]
Next, we need to determine the domain and range of \( f^{-1}(x) \).
### Domain of \( f^{-1}(x) \):
The domain of \( f^{-1}(x) \) is determined by the values of \( x \) for which the function is defined. The function \( f^{-1}(x) = \frac{7 - 8x}{x + 5} \) is undefined when the denominator is zero:
\[
x + 5 = 0 \implies x = -5
\]
Thus, the domain of \( f^{-1}(x) \) is all real numbers except \( -5 \):
\[
\text{Domain of } f^{-1}: (-\infty, -5) \cup (-5, \infty)
\]
### Range of \( f^{-1}(x) \):
The range of \( f^{-1}(x) \) corresponds to the domain of \( f(x) \). To find the domain of \( f(x) \), we note that \( f(x) \) is defined for all \( x \) except when the denominator is zero:
\[
8 + x = 0 \implies x = -8
\]
Thus, the domain of \( f(x) \) is all real numbers except \( -8 \):
\[
\text{Domain of } f: (-\infty, -8) \cup (-8, \infty)
\]
Since \( f \) is a one-to-one function, the range of \( f \) is the same as the domain of \( f^{-1} \). Therefore, the range of \( f^{-1}(x) \) is:
\[
\text{Range of } f^{-1}: (-\infty, -8) \cup (-8, \infty)
\]
### Final Answers:
\[
f^{-1}(x) = \frac{7 - 8x}{x + 5}
\]
\[
\text{Domain of } f^{-1}: (-\infty, -5) \cup (-5, \infty)
\]
Quick Answer
\( f^{-1}(x) = \frac{7 - 8x}{x + 5} \)
Domain of \( f^{-1}: (-\infty, -5) \cup (-5, \infty) \)
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