- #1
buffordboy23
- 548
- 2
Show that
[tex] \sum^{\infty}_{n=0} p^{n}cos\left(n\theta\right) = \frac{1-pcos\theta}{1-2pcos\theta+p^{2}} [/tex]
if [tex] \left|p\right|<1[/tex].
Looking at this series, I see that p will approach zero as n approaches infinity, while the series oscillates because of the cosine term. The convergence is easy to see, but not the function that it converges to. The series is reminiscent of a geometric series, or possibly a Fourier series, but the cosine term really complicates things for me. I tried looking for similar problems on the web, but only found examples that apply the tests of convergence rather than determining this function.
[tex] \sum^{\infty}_{n=0} p^{n}cos\left(n\theta\right) = \frac{1-pcos\theta}{1-2pcos\theta+p^{2}} [/tex]
if [tex] \left|p\right|<1[/tex].
Looking at this series, I see that p will approach zero as n approaches infinity, while the series oscillates because of the cosine term. The convergence is easy to see, but not the function that it converges to. The series is reminiscent of a geometric series, or possibly a Fourier series, but the cosine term really complicates things for me. I tried looking for similar problems on the web, but only found examples that apply the tests of convergence rather than determining this function.