How this inequality is derived?












1












$begingroup$


Let $T$$ℓ_2$$ℓ_2$ be defined by
$T((x_1,x_2,...,x_n...))$=$(X_2-X_1, X_3-X_2,...,X_{n+1}-x_n,...)$
Then I have find the norm of $T$.



Here is the answer to this question: https://math.stackexchange.com/a/1647794/581242



I am not able to see how this first inequality is derived.



$|(Tx)| = sqrt{sum_{i=1}^infty |x_{i+1}-x_i|^2} leq
sqrt{sum_{i=1}^infty |x_{i+1}|^2 + sum_{i=1}^infty|x_i|^2} leq 2|x|$










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    Hint: apply Minkowski's inequality.
    $endgroup$
    – Victoria M
    Jan 26 at 0:47










  • $begingroup$
    The first inequality is wrong. @StammeringMathematician
    $endgroup$
    – Kavi Rama Murthy
    Jan 26 at 0:49










  • $begingroup$
    @KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:53










  • $begingroup$
    @KaviRamaMurthy Is this an application of Minkowski's inequality.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:54


















1












$begingroup$


Let $T$$ℓ_2$$ℓ_2$ be defined by
$T((x_1,x_2,...,x_n...))$=$(X_2-X_1, X_3-X_2,...,X_{n+1}-x_n,...)$
Then I have find the norm of $T$.



Here is the answer to this question: https://math.stackexchange.com/a/1647794/581242



I am not able to see how this first inequality is derived.



$|(Tx)| = sqrt{sum_{i=1}^infty |x_{i+1}-x_i|^2} leq
sqrt{sum_{i=1}^infty |x_{i+1}|^2 + sum_{i=1}^infty|x_i|^2} leq 2|x|$










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    Hint: apply Minkowski's inequality.
    $endgroup$
    – Victoria M
    Jan 26 at 0:47










  • $begingroup$
    The first inequality is wrong. @StammeringMathematician
    $endgroup$
    – Kavi Rama Murthy
    Jan 26 at 0:49










  • $begingroup$
    @KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:53










  • $begingroup$
    @KaviRamaMurthy Is this an application of Minkowski's inequality.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:54
















1












1








1





$begingroup$


Let $T$$ℓ_2$$ℓ_2$ be defined by
$T((x_1,x_2,...,x_n...))$=$(X_2-X_1, X_3-X_2,...,X_{n+1}-x_n,...)$
Then I have find the norm of $T$.



Here is the answer to this question: https://math.stackexchange.com/a/1647794/581242



I am not able to see how this first inequality is derived.



$|(Tx)| = sqrt{sum_{i=1}^infty |x_{i+1}-x_i|^2} leq
sqrt{sum_{i=1}^infty |x_{i+1}|^2 + sum_{i=1}^infty|x_i|^2} leq 2|x|$










share|cite|improve this question









$endgroup$




Let $T$$ℓ_2$$ℓ_2$ be defined by
$T((x_1,x_2,...,x_n...))$=$(X_2-X_1, X_3-X_2,...,X_{n+1}-x_n,...)$
Then I have find the norm of $T$.



Here is the answer to this question: https://math.stackexchange.com/a/1647794/581242



I am not able to see how this first inequality is derived.



$|(Tx)| = sqrt{sum_{i=1}^infty |x_{i+1}-x_i|^2} leq
sqrt{sum_{i=1}^infty |x_{i+1}|^2 + sum_{i=1}^infty|x_i|^2} leq 2|x|$







functional-analysis normed-spaces






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Jan 26 at 0:43









StammeringMathematicianStammeringMathematician

2,5881324




2,5881324








  • 1




    $begingroup$
    Hint: apply Minkowski's inequality.
    $endgroup$
    – Victoria M
    Jan 26 at 0:47










  • $begingroup$
    The first inequality is wrong. @StammeringMathematician
    $endgroup$
    – Kavi Rama Murthy
    Jan 26 at 0:49










  • $begingroup$
    @KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:53










  • $begingroup$
    @KaviRamaMurthy Is this an application of Minkowski's inequality.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:54
















  • 1




    $begingroup$
    Hint: apply Minkowski's inequality.
    $endgroup$
    – Victoria M
    Jan 26 at 0:47










  • $begingroup$
    The first inequality is wrong. @StammeringMathematician
    $endgroup$
    – Kavi Rama Murthy
    Jan 26 at 0:49










  • $begingroup$
    @KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:53










  • $begingroup$
    @KaviRamaMurthy Is this an application of Minkowski's inequality.
    $endgroup$
    – StammeringMathematician
    Jan 26 at 0:54










1




1




$begingroup$
Hint: apply Minkowski's inequality.
$endgroup$
– Victoria M
Jan 26 at 0:47




$begingroup$
Hint: apply Minkowski's inequality.
$endgroup$
– Victoria M
Jan 26 at 0:47












$begingroup$
The first inequality is wrong. @StammeringMathematician
$endgroup$
– Kavi Rama Murthy
Jan 26 at 0:49




$begingroup$
The first inequality is wrong. @StammeringMathematician
$endgroup$
– Kavi Rama Murthy
Jan 26 at 0:49












$begingroup$
@KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
$endgroup$
– StammeringMathematician
Jan 26 at 0:53




$begingroup$
@KaviRamaMurthy Thanks for pointing that out. Now I can see it after your answer below.
$endgroup$
– StammeringMathematician
Jan 26 at 0:53












$begingroup$
@KaviRamaMurthy Is this an application of Minkowski's inequality.
$endgroup$
– StammeringMathematician
Jan 26 at 0:54






$begingroup$
@KaviRamaMurthy Is this an application of Minkowski's inequality.
$endgroup$
– StammeringMathematician
Jan 26 at 0:54












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$begingroup$

It appears that there was a small typo. Use the inequality $|a-b|^{2} leq 2(a^{2}+b^{2})$ . The final result is correct but the first inequality is wrongly stated.






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    $begingroup$

    It appears that there was a small typo. Use the inequality $|a-b|^{2} leq 2(a^{2}+b^{2})$ . The final result is correct but the first inequality is wrongly stated.






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      It appears that there was a small typo. Use the inequality $|a-b|^{2} leq 2(a^{2}+b^{2})$ . The final result is correct but the first inequality is wrongly stated.






      share|cite|improve this answer









      $endgroup$
















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        1





        $begingroup$

        It appears that there was a small typo. Use the inequality $|a-b|^{2} leq 2(a^{2}+b^{2})$ . The final result is correct but the first inequality is wrongly stated.






        share|cite|improve this answer









        $endgroup$



        It appears that there was a small typo. Use the inequality $|a-b|^{2} leq 2(a^{2}+b^{2})$ . The final result is correct but the first inequality is wrongly stated.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 26 at 0:47









        Kavi Rama MurthyKavi Rama Murthy

        68.8k53169




        68.8k53169






























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