How to prove that this series bounded and monotonic

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Homework Help Overview

The discussion revolves around proving properties of a series defined by the product \( X_n = (1 - \frac{1}{2})(1 - \frac{1}{4}) \ldots (1 - \frac{1}{2^n}) \). Participants are exploring whether the series is bounded and monotonic, specifically focusing on its behavior as \( n \) increases.

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  • Mixed

Approaches and Questions Raised

  • Participants discuss attempts to prove monotonicity by comparing terms and expressing \( 1 - \frac{1}{2^n} \) in a different form. There are questions about whether the series is increasing or decreasing, with some suggesting it is increasing based on the sequence of terms. Others clarify the definition of the sequence, leading to further exploration of its behavior.

Discussion Status

There is an ongoing exploration of the sequence's properties, with some participants asserting that it is decreasing while others provide insights into its bounds. Guidance has been offered regarding the relationship between consecutive terms, but no consensus has been reached on the overall boundedness of the series.

Contextual Notes

Participants are navigating assumptions about the sequence's behavior and its definition, which may influence their reasoning about boundedness and monotonicity. There is a mention of specific values that could serve as bounds, but these are still under discussion.

transgalactic
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Xn=(1-1/2)(1-1/4)..(1-(1/(2^n))

i tried to prove that its monotonic
by :
1-1/(2^n) = (2^n-1)/2^n

2^n -1 <2^n
obviously its correct
the numerator of each object is smaller then the denominator.

what now??

and how to prove that its bounded?
 
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You need to show that [tex]x_n > x_{n+1}[/tex] for all n given that [tex]x_n(1-2^{-n}) = x_{n+1}[/tex]

It should be fairly easy from here
 
that proves that its monotonic
how to prove that its bounded?
 
Is it increasing or decreasing?
 
each next member is bigger then the previous one
so its increasing

1-1/2 1-1/4 1-1/8 etc..
 
That's now what the sequence is. The sequence is

1/2, 1/2*3/4, 1/2*3/4*7/8 etc.

you should be able to see this from how xn is defined.
 
ok so it getting smaller and smaller
how to prove that its bounded?
 
There's a pretty obvious lower bound. And since it is decreasing, isn't x1= 1/2 an upper bound?
 

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