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 33127 by prof Abdo imad last updated on 10/Apr/18

$$find\sum _{n=0}^{\mathrm{\infty }}\frac{sin\left(na\right)}{{\left(sina\right)}^n}\frac{x^n}{n!}with0<a<\pi .$$

Commented byprof Abdo imad last updated on 12/Apr/18

$$S\left(x\right)=Im\left(\sum _{n=0}^{\mathrm{\infty }}\frac{e^{ina}{x}^n}{n!{\left(sina\right)}^n}\right)but$$ $$w\left(x\right)=\sum _{n=0}^{\mathrm{\infty }}\frac{e^{ina}{x}^n}{n!{\left(sina\right)}^n}=\sum _{n=0}^{\mathrm{\infty }}\frac{1}{n!}{\left(\frac{e^{ia}x}{sina}\right)}^n$$ $$butwehave\sum _{n=0}^{\mathrm{\infty }}\frac{u^n}{n!}=e^u\mathrm{\forall }u\in C\Rightarrow$$ $$w\left(x\right)=e^{\frac{e^{ia}}{sina}x}=e^{\frac{x}{sina}(coa+isina)}$$ $$=e^{\frac{xcosa}{sins}}{e}^{ix}=e^{\frac{xcosa}{sina}}(cosx+isinx)\Rightarrow$$ $$S\left(x\right)=sinx{e}^{\frac{xcosa}{sina}}.$$

Terms of Service

Privacy Policy

Contact: info@tinkutara.com