The inverse of a function is given by \(f^{-1} : x \to \frac{x + 1}{4}\).

  • A \(f : x \to 4x - 1\)
  • B \(f : x \to 4x + 1\)
  • C \(f : x \to \frac{4x - 1}{4}\)
  • D \(f : x \to \frac{x - 1}{2}\)
waec 2011furthermathematics

The correct answer is A. \(f : x \to 4x - 1\)

The inverse of the inverse of a function gives the function 

i.e \(f^{-1}(f^{-1}(x)) = f(x)\)

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

Take y = x, so

\(f^{-1}(y) = \frac{y + 1}{4}\)

Let \(x = f^{-1}(y)\),

\(x = \frac{y + 1}{4} \implies 4x = y + 1\)

\(y = f(x) = 4x - 1\)

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