Example 4.23. The
infinite series
has
radius of convergence
by the ratio test because
.
Since the limit equals 0, we
set
.
Explore Solution 4.23.
Enter the formula for the coefficients.
![[Graphics:../Images/ComplexPowerSeriesMod_gr_102.gif]](../Images/ComplexPowerSeriesMod_gr_102.gif)
Use d'Alembert's ratio test and find the limit and then the radius of convergence R.
![[Graphics:../Images/ComplexPowerSeriesMod_gr_104.gif]](../Images/ComplexPowerSeriesMod_gr_104.gif)
The sum of the series is a well known function.
![]()
We can plot some of the partial sums and see that they converge to f[z].
![[Graphics:../Images/ComplexPowerSeriesMod_gr_108.gif]](../Images/ComplexPowerSeriesMod_gr_108.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_110.gif]](../Images/ComplexPowerSeriesMod_gr_110.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_112.gif]](../Images/ComplexPowerSeriesMod_gr_112.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_114.gif]](../Images/ComplexPowerSeriesMod_gr_114.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_116.gif]](../Images/ComplexPowerSeriesMod_gr_116.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_119.gif]](../Images/ComplexPowerSeriesMod_gr_119.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_121.gif]](../Images/ComplexPowerSeriesMod_gr_121.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_123.gif]](../Images/ComplexPowerSeriesMod_gr_123.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_125.gif]](../Images/ComplexPowerSeriesMod_gr_125.gif)
![[Graphics:../Images/ComplexPowerSeriesMod_gr_127.gif]](../Images/ComplexPowerSeriesMod_gr_127.gif)