Combined Function Analysis: Domain and Inversion Reflection

00:00 7 marks

  • Exam Style - Paper 1
  • SL
  • Tier 3
  • Inverse Functions
  • One-to-one Functions
  • Composite functions
  • Domain of functions

Consider the functions \(f(x)= x^2-1\) and \(g(x)= \ln(x)\). Define the composite function \(h(x)= g(f(x)) = \ln(x^2-1)\).

(a) Determine the domain of \(h(x)\).

(b) Assuming \(h(x)\) is invertible on an appropriately restricted domain, find the expression for its inverse function \(h^{-1}(x)\).

(c) Discuss briefly how the domain restrictions of \(h(x)\) affect the existence of an inverse function.

Part a

3 minutes 2 marks

Question

Determine the domain of the composite function \(h(x)= \ln(x^2-1)\). Give your answer in interval notation.



Hint Hint

Hint

Set the inequality \(x^2-1 > 0\) and solve for \(x\).

  • Answer Answer

Complete Answer

The domain of \(h(x)\) is \(x \in (-\infty, -1) \cup (1, \infty)\).

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  • Answer Explanation Answer Explanation

Part b

4 minutes 3 marks

Question

Assuming \(h(x)= \ln(x^2-1)\) is invertible on a restricted domain, find the expression for its inverse function \(h^{-1}(x)\) on that domain.



Hint Hint

Hint

Set \(y = \ln(x^2-1)\) and solve for \(x\) by exponentiating both sides, then choose the appropriate branch.

  • Answer Answer

Complete Answer

\(h^{-1}(x) = \sqrt{e^x+1}\)

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  • Answer Explanation Answer Explanation

Part c

3 minutes 2 marks

Question

Discuss briefly how the domain restrictions of \(h(x)= \ln(x^2-1)\) affect the existence of an inverse function. In your answer, explain any limitations that arise from the composite function’s domain.



Hint Hint

Hint

Consider the fact that \(h(x)\) is not one-to-one without restricting its domain.

  • Answer Answer

Complete Answer

The inverse exists only on a restricted domain where \(h(x)\) is one-to-one, such as \(x>1\) or \(x<-1\).

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