Euler's Method of Trigonometric Series- Real Analysis

[AnnieF]

Homework Statement

Use Equation (1) to derive the formula: (1-a*cos(phi))/(1-2*a*cos(phi)+a^2))= 1+a*cos(phi)+a^2(cos(2phi))+a^3(cos(3phi))...

Homework Equations

Equation (1) is 1/(1-a(cos(phi)+isin(phi)))= 1+ [a(cos(phi)+isin(phi)]+ [a(cos(phi)+isin(phi)]^2 + [a(cos(phi)+isin(phi)]^3...

The Attempt at a Solution

I know that you are supposed to somehow use that (cos(phi)+isin(phi))^k= cos(kphi)+ isin(kphi), but I'm not sure how to go about this at all. Please help!

 

[micromass]

It would help us greatly if you were to use LaTeX in your post: https://www.physicsforums.com/showpost.php?p=3977517&postcount=3
Right now, I'm not going to reply since I'm not going to take the effort of decyphering your post.