Thursday, 8 June 2017

logarithms - Show that $ln(1+x)=ln x+frac{1}{x}-frac{1}{2x^2}+frac{1}{3x^3}-frac{1}{4x^4}+cdots$ when $x>1$





If $x>1$ show that $\ln(1+x)=\ln x+\frac{1}{x}-\frac{1}{2x^2}+\frac{1}{3x^3}-\frac{1}{4x^4}+\cdots$




I know from binomial expansion that $(1+x)$ will produce a divergent series in the form of $1-x+x^2-x^3+\cdots$ but I don't know how to apply that in this situation.



Do I just need to integrate $\ln(1-x+x^2+\cdots$)? If so, why integrate? What role does integration have here?


Answer



Hint: Expand $\ln(1+x)-\ln(x)=\ln(1+u)$ into a power series in $u=1/x$ with $|u|\lt1$.



No comments:

Post a Comment

real analysis - How to find $lim_{hrightarrow 0}frac{sin(ha)}{h}$

How to find $\lim_{h\rightarrow 0}\frac{\sin(ha)}{h}$ without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...