- #1

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Does it actually converge or diverge??? Why?

Thanks

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- Thread starter zmike
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- #1

- 102

- 0

Does it actually converge or diverge??? Why?

Thanks

- #2

dx

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Hi zmike,

It doesn't converge:

1 = 1

1 + (-1) = 0

1 + (-1) + 1 = 1

1 + (-1) + 1 + (-1) = 0

It keeps oscillating between 1 and 0.

It doesn't converge:

1 = 1

1 + (-1) = 0

1 + (-1) + 1 = 1

1 + (-1) + 1 + (-1) = 0

It keeps oscillating between 1 and 0.

Last edited:

- #3

- 102

- 0

Hi zmike,

It doesn't converge:

1 = 1

1 + (-1) = 0

1 + (-1) + 1 = 1

1 + (-1) + 1 + (-1) = 0

It keeps oscillating between 1 and 0.

thanks, just one more thing,

so for ratio test, root test, test for divergence ALL work for alternating series? I am asking this b/c my textbook says they only work for positive sequences

also can I seperate a sum? so can I take

[sigma an] * [sigma bn] = sigma (an*bn)? If not, wouldn't that violate the properties of limits?

Thanks

- #4

dx

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The ratio test applies only to positive series.

For finite sums (∑a)(∑b) = ∑∑(ab) is true.

For finite sums (∑a)(∑b) = ∑∑(ab) is true.

- #5

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What does the ∑∑ mean? take the sum twice? so is this also true with infinite sums?

also, does this mean that if either a or b is divergent, I can conclude that the series is divergent?

thanks

- #6

dx

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Sorry about the confusing notation. Latex is not working currently and I didn't know how to write it.

Sum(i = 1 to n)[A_i] x Sum(j = 1 to m)[B_j] equals Sum(i = 1 to n)Sum(j = 1 to m)[A_i B_j]

For infinite series, if both the series are convergent, this will still work. If either of them is divergent, then clearly the left hand side is not defined.

Sum(i = 1 to n)[A_i] x Sum(j = 1 to m)[B_j] equals Sum(i = 1 to n)Sum(j = 1 to m)[A_i B_j]

For infinite series, if both the series are convergent, this will still work. If either of them is divergent, then clearly the left hand side is not defined.

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