The important fact that ends the section is this: If AT Ax = 0 then Ax = O. New Proof
Chapter 4, Problem 27(choose chapter or problem)
The important fact that ends the section is this: If AT Ax = 0 then Ax = O. New Proof: The vector Ax is in the nullspace of . Ax is always in the column space of . To be in both of those perpendicular spaces, Ax must be zero.
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