How do you find the derivative of y=ln(cos(x))y=ln(cos(x)) ?

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asked May 24, 2015 177k views

2 votes

How do you find the derivative of y=ln(cos(x))y=ln(cos(x)) ?

Mathematics
high-school

Tiago Santos asked

by Tiago Santos

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$y=ln(cosx)\\\\We\ know:\\(lnx)'=(1)/(x)\ and\ (cosx)'=-sinx\ and\ \{f[g(x)]\}'=f'[g(x)]\cdot g'(x)\\\\therefore:\\\\y'=(1)/(cosx)\cdot(-sinx)=-(sinx)/(cosx)=-tanx$

Lidashuang answered May 31, 2015

by Lidashuang

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