Question and Answers Forum

All Questions      Topic List

Relation and Functions Questions

Previous in All Question      Next in All Question      

Previous in Relation and Functions      Next in Relation and Functions      

Question Number 121490 by mathmax by abdo last updated on 08/Nov/20

$$\mathrm{let}\mathrm{f}\left(\mathrm{x}\right)=\ln \left(\mathrm{tanx}\right)$$$$\mathrm{developp}\mathrm{f}\mathrm{at}\mathrm{fourier}\mathrm{serie}$$

Answered by mnjuly1970 last updated on 08/Nov/20

$$1.f\left(x\right)=ln\left(2sin\left(x\right)\right)\stackrel{fourierseries}{=}\underset{n=1}{\sum ^{\mathrm{\infty }}}\frac{-1}{n}cos\left(2nx\right)$$$$2.f\left(x\right)=ln\left(2cos\left(x\right)\right)\stackrel{fourierseries}{=}\underset{n=1}{\sum ^{\mathrm{\infty }}}\frac{{(-1))}^{n+1}}{n}cos\left(2nx\right)$$$$from\left(1\right)\mathrm{\&}\left(2\right):ln\left(tan\left(x\right)\right)\stackrel{fourierseries}{=}\underset{n=1}{\sum ^{\mathrm{\infty }}}\frac{-2}{(2n-1)}cos\left((4n-2)x\right)$$$$toolsforproof:$$$$i:sin\left(x\right)=\frac{e^{ix}-e^{-ix}}{2i}$$$$ii:cos\left(x\right)=\frac{e^{ix}+e^{-ix}}{2}$$$$iii:ln(1-z)=-\underset{n=1}{\sum ^{\mathrm{\infty }}}\frac{z^n}{n}$$$$iv:ln(1+z)=\underset{n=1}{\sum ^{\mathrm{\infty }}}\frac{{(-1)}^{n-1}{z}^n}{n}$$$$...m.n.1970...$$

Terms of Service

Privacy Policy

Contact: info@tinkutara.com