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phospho
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This is from the haggarty book on analysis
take the set ## S := \{ 2^{-m} + 3^{-n} + 5^{-p} | m,n,p \in \mathbb{N} \} ##
claim [itex] inf(S) = 0 [/itex]
proof by contradiction:
suppose ## A > 0 ## where A is the largest lower bound for S
then ## 1/2^m + 1/3^n + 1/5^p \geq A ##
i.e. ## 2^m + 3^n + 5^p \geq A(2^m3^n5^p) ##
let ## X = 2^m + 3^n + 5^p ## and ## Y = 2^m3^n5^p ## where ## Y,X \in \mathbb{N} ##
then ## X \geq AY ## hence ## Y \leq \frac{X}{A} ## which is a contradiction to the archimedean postulate which states for any real x a natural number n >= x hence the lower bound is 0
is this proof OK or have I gone wrong somewhere?
take the set ## S := \{ 2^{-m} + 3^{-n} + 5^{-p} | m,n,p \in \mathbb{N} \} ##
claim [itex] inf(S) = 0 [/itex]
proof by contradiction:
suppose ## A > 0 ## where A is the largest lower bound for S
then ## 1/2^m + 1/3^n + 1/5^p \geq A ##
i.e. ## 2^m + 3^n + 5^p \geq A(2^m3^n5^p) ##
let ## X = 2^m + 3^n + 5^p ## and ## Y = 2^m3^n5^p ## where ## Y,X \in \mathbb{N} ##
then ## X \geq AY ## hence ## Y \leq \frac{X}{A} ## which is a contradiction to the archimedean postulate which states for any real x a natural number n >= x hence the lower bound is 0
is this proof OK or have I gone wrong somewhere?