On which of these intervals is $\cos x$ strictly decreasing?

(- \frac{\pi}{2}, \frac{\pi}{2})

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(\pi, 2 \pi)

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(0, \pi)

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(\frac{\pi}{2}, \frac{3 \pi}{2})

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Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

The derivative is $- \sin x$ .
It is negative throughout $(0, \pi)$ , and changes sign inside each of the others.

Ten questions from Increasing & Decreasing Functions, at your own pace.

Ten questions from Increasing & Decreasing Functions, at your own pace.

On which of these intervals is cos⁡x\cos xcosx strictly decreasing?