# Caracterizing a subspace of L^2

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[SOLVED] Caracterizing a subspace of L^2

1. Homework Statement

Call M the subspace of L²([0,1]) consisting of all functions of vanishing mean. I.e., $u\in M \Rightarrow \int_0^1u(s)ds=0$.

I am trying to find the dimension of the orthogonal of M,

$$M^{\perp}=\{x\in L^2([0,1]):\int_0^1x(s)u(s)ds=0 \ \forall u\in M\}$$

I would be surprised if $M^{\perp}$ was anything other than the constant functions, but my attempts at a proof have been unsuccessful.

Any idea how to go at this?

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Solved.

Last edited:
morphism
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Was it the (a.e.) constant functions in the end?

Sorry I couldn't help -- been busy with studying for my finals!

Dick
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Was it the (a.e.) constant functions in the end?

Sorry I couldn't help -- been busy with studying for my finals!
How could it be anything else? The set of vanishing mean functions is basically defined as the set of all u(x) such that <u(x),1>=0. L^2 is a norm up to a.e.

morphism