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Question
If f(x) = |cos x|, find f'`((3pi)/4)`
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Solution
When `pi/2` < x , pi, cos x < 0`
So that |cos x| = `- cos x`
i.e., f(x) = `- cos x`
⇒ f'(x) = sin x.
Hence, `"f'"((3pi)/4) = sin ((3pi)/4) = 1/sqrt(2)`
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