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 convergentserieswith
and. Then and are also convergentwhere
and
(The sum or differenceof convergentseriesis also convergent.)2. Let c ≠ 0 be a constant.Suppose
convergesand Then also convergeswhere. If
diverges,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