# Differentiate yourself in trigonometry

Calculus Level 3

$y = \cos(x) \cdot \ln \left(\frac{\sin(x)+1}{\cos(x)} \right)$

Find the value of the constant $$a$$ if $$y + y'' = a \cdot \tan(x)$$.

Note: By $$y''$$ we mean the 'second derivative' of $$y$$.

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