How do you show that M double perp is a subset of M?
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 Rn then T(X) = projU(X) for all X in Rn.
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 :)