What is the derivative of $ln(cosx)$ ?

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Answer 1 · 2015-10-16T20:58:47

$-tanx$

Rule : $d/dxlnu(x)=1/u*(du)/dx$

$therefore d/dx ln(cosx)=1/cosx*d/(dx)cosx$

$=1/cosx*-sinx$

$=-sinx/cosx$

$=-tanx$

What is the derivative of ln(cosx) ln(cosx)?