I am having problem with a question regarding Maclaurin expansion.
a) Find the term up to $x^4$ in the Maclaurin expansion of $f(x)=\ln(\cos(x))$.
This part I was able to anwser part a. The Maclaurin expansion until $x^4$ is: $f(x)=-x^2/2-x^4/12$
b) Use this series to find an approximation in terms of $\pi$ for $\ln(2)$.
I was not able to answer part b. If someone know how to make it I would appreciate it.