Rational Function Analysis and Reflection

00:00 10 marks

  • Exam Style - 2
  • SL & HL
  • Tier 3
  • Asymptotes
  • Rational functions
  • Inverse Functions
  • Domain identification
  • Reflection of graphs

Consider the rational function \(f(x) = \frac{2x – 3}{x + 4}\).

(a) Determine the domain of \(f(x)\) and identify any vertical asymptotes.

(b) Find the inverse function \(f^{-1}(x)\) algebraically.

(c) Describe the reflection process used to obtain the graph of \(f^{-1}(x)\) from the graph of \(f(x)\).

Part a

4 minutes 3 marks

Question

Determine the domain of \(f(x) = \frac{2x – 3}{x + 4}\) and identify any vertical asymptotes.



Hint Hint

Hint

Set the denominator equal to zero to find the exclusion in the domain and the vertical asymptote.

  • Answer Answer

Complete Answer

The domain is \(\{x \in \mathbb{R} : x
eq -4\}\) with a vertical asymptote at \(x = -4\).

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Part b

4 minutes 3 marks

Question

Find the inverse function \(f^{-1}(x)\) of \(f(x) = \frac{2x – 3}{x+4}\) algebraically.



Hint Hint

Hint

Swap \(x\) and \(y\) to get \(x = \frac{2y – 3}{y+4}\) and then solve for \(y\).

  • Answer Answer

Complete Answer

\(f^{-1}(x)=\frac{3+4x}{2-x}\)

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Part c

4 minutes 4 marks

Question

Describe how you would sketch the graph of \(f^{-1}(x)=\frac{3+4x}{2-x}\) using the reflection of \(f(x)=\frac{2x-3}{x+4}\) about the line \(y=x\).



Hint Hint

Hint

Remember that the graph of an inverse function is the mirror image of the original function across the line \(y = x\).

  • Answer Answer

Complete Answer

Reflect the graph of \(f(x)=\frac{2x-3}{x+4}\) across the line \(y=x\) by swapping each point \((a, b)\) to \((b, a)\). The key features such as asymptotes and intercepts are also reflected accordingly.

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