Usingthenth-Term Test,. Sincethe limit is 0, we cannotmakea conclusionaboutconvergence
or divergence.
Rulesfor ConvergentSeries,Reindexing
Rules
As with sequences,thereare rulesfor convergentinfiniteseriesthat help makeit easierto determinecon-
vergence.
Theorem(Rulesfor ConvergentSeries)1. Suppose and are convergentserieswithand. Then and are also convergentwhereand(The sum or differenceof convergentseriesis also convergent.)2. Let c ≠ 0 be a constant.Supposeconvergesand Then also convergeswhere. Ifdiverges,then also diverges.(Multiplyingby a nonzeroconstantdoesnot affect convergenceor
divergence.)Example 10
Find the sum of.
Solution
Usingthe RulesTheorem,.
is a convergentgeometricserieswitha= 2 and. Its sum is.is a convergentgeometricserieswitha= 2 and. Its sum is.Then