The function \(f\) is such that \(f(x) = (3x + 2)^3 - 5\) for \(x \geq 0\).
Obtain an expression for \(f^{-1}(x)\) and state the domain of \(f^{-1}\).
Solution
Let \(y = f(x) = (3x + 2)^3 - 5\).
To find \(f^{-1}(x)\), solve for \(x\) in terms of \(y\):
\(y = (3x + 2)^3 - 5\)
Add 5 to both sides: \(y + 5 = (3x + 2)^3\)
Take the cube root: \(\sqrt[3]{y + 5} = 3x + 2\)
Subtract 2: \(\sqrt[3]{y + 5} - 2 = 3x\)
Divide by 3: \(x = \frac{\sqrt[3]{y + 5} - 2}{3}\)
Thus, \(f^{-1}(x) = \frac{\sqrt[3]{x + 5} - 2}{3}\).
The domain of \(f^{-1}\) is the range of \(f\), which is \(x \geq 3\).
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