Q17 of 168 Page 205

Prove that the function f given by f (x) = log |cos x| is strictly decreasing onand strictly increasing on.

It is given that f (x) = log |cos x|


In interval, f’(x) = -tanx < 0


Therefore, f is strictly decreasing on.


In interval, f’(x) = -tanx > 0


Therefore, f is strictly increasing in.


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