Summary Of Convergence Tests For Series

  • October 2019
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Summary of Convergence Tests for Series Test term test (or the zero test) n

Series

X

th

Geometric series

1 X n

=0

or

n

ax

-series

n

=1

n

1 X

1 X

=1

n

ax

1

!

Comparison

an

and

n

Root*

X X

an

!1 bn

with lim

an

with lim

X

bn

a

1 X

!1

X

bn

n

=1

j

an

X

+1 j = L

j nj a

p n j j= n n!1 a

Z1

Z 1c

( ) dx converges

f x

( ) dx diverges

bn

converges =)

an

diverges =)

bn

converges =)

bn

diverges =)

X

X

bn

X

X

an

diverges

an

an

converges

converges

diverges

Converges (absolutely) if L < 1 Diverges if L > 1 or if L is in nite

Diverges if L > 1 or if L is in nite

X (an > 0)

j n j converges =) a

X

an

converges

Converges if 0 < an+1 < an for all n and lim an = 0 n

!1

Useful for comparison tests if the nth term an of a series is similar to axn .

n

f x

c

!1 an = 0.

Useful for comparison tests if the nth term an of 1 a series is similar to p .

Converges (absolutely) if L < 1 L

an

( 1)n 1 an

X

=L>0

n

X

j nj

Alternating series

X

an

Absolute Value

X

Diverges if

with an ; bn > 0 for all n and lim

Ratio

Converges if

with 0  an  bn for all n

X

Limit Comparison*

X

and

only if jxj < 1

Diverges if p  1

p

an (c  0) = an = f (n) for all n

an

x

n

Converges if p > 1

n c

X

a

1

Inconclusive if lim

Diverges if jxj  1

1 X

Integral

!1 an 6= 0

Converges to

1 n

Comments

Diverges if lim

an

n

p

Convergence or Divergence

The function f obtained from an = f (n) must be continuous, positive, decreasing and readily integrable for x  c. The X comparison series bn is often a geometric series or a p-series. The X comparison series bn is often a geometric series or a p-series. To nd bn consider only the terms of an that have the greatest e ect on the magnitude. Inconclusive if L = 1. Useful if an involves factorials or nth powers. Test is inconclusive if L = 1. Useful if an involves th n powers. Useful for series containing both positive and negative terms. Applicable only to series with alternating terms.

*The Root and Limit Comparison tests are not included in the current textbook used in Calculus classes at Bates College.

1

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