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## Homework Statement

How do you show that M double perp is a subset of M?

## Homework Equations

## The Attempt at a Solution

My prof told me to try proving that M is a subset of M perp perp, then to use the facts that if M is a subspace of R

^{n}then T(X) = proj

_{U}(X) for all X in R

^{n}.

I'm not sure how to go about that. I know logically that it's a subset, but I don't know how to prove it.

I'm thinking that once I prove it, maybe I can show that the dimension of U and U perp perp are equal, so the spaces are equal too?

Can anyone help get me started? Thanks :)

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