Homework Help: An unusually easy proof of vector.

1. Sep 18, 2011

athrun200

1. The problem statement, all variables and given/known data
See the attachment.

2. Relevant equations

3. The attempt at a solution

It seems this proof is trivial, too easy that I am not sure if I do it correctly.

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2. Sep 18, 2011

HallsofIvy

Yes, it is too trivial

You start by saying $||u||_\infty= |u_n|$. You can't do that $||u||_\infty$ is the largest component, not necessarily the nth component

You can say $||u||_\infty\le |u_n|$. Does that help?