WAEC 2020 · Paper 1 · Q29

Applications of differentiation

In what interval is the function $f : x \to 2x - x^2$ increasing?

Worked solution (try it first)

A function increases where its gradient is positive.
Here $f'(x) = 2 - 2x$ .
Solve $2 - 2x > 0$ : $2 > 2x$ , so $x < 1$ .
So $f$ is increasing for $x < 1$ , option B.

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