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Nov 2023 p13 q7
745
The function \(f\) is defined by \(f(x) = 1 + \frac{3}{x-2}\) for \(x > 2\).
(a) State the range of \(f\).
(b) Obtain an expression for \(f^{-1}(x)\) and state the domain of \(f^{-1}\).
Solution
(a) The function \(f(x) = 1 + \frac{3}{x-2}\) has a vertical asymptote at \(x = 2\) and a horizontal asymptote at \(y = 1\). As \(x \to \infty\), \(f(x) \to 1\). Therefore, the range of \(f\) is \(y > 1\).
(b) To find \(f^{-1}(x)\), start with \(y = 1 + \frac{3}{x-2}\).
Rearrange to find \(x\):
\(y - 1 = \frac{3}{x-2}\)
\((x-2)(y-1) = 3\)
\(x-2 = \frac{3}{y-1}\)
\(x = \frac{3}{y-1} + 2\)
Thus, \(f^{-1}(x) = \frac{3}{x-1} + 2\).
The domain of \(f^{-1}\) is \(x > 1\) because the original range of \(f\) was \(y > 1\).