WAEC 2020 · Paper 1 · Q11

Functions

Given that $f(x) = 2x$ and $g(x) = 3x^2$ , find the values of $x$ for which $f^{-1}(x) = g(x)$ .

Worked solution (try it first)

The inverse of doubling is halving: $f^{-1}(x) = \dfrac{x}{2}$ .
Set $\dfrac{x}{2} = 3x^2$ and multiply by 2: $x = 6x^2$ , so $x(6x - 1) = 0$ .
So $x = 0$ or $x = \frac{1}{6}$ , option A.

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