# Logarithmic and Trigonometric Bifunctional Derivative

Calculus Level 3

Given that $$f(x) = \ln (\cos(x) \tan(x) )$$. It is defined on the subset of reals where the expression is valid.

Find the first derivative of $$f(x)$$ i.e., $$f'(x)$$ at $$x = \dfrac{\pi }{4}$$.

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