are the following statements true or false? ? 1. if , where is in a subspace and is in , then must be the orthogonal projection of onto . ? 2. let be an orthonormal basis of a vector space . in the orthogonal decomposition theorem, each term is itself an orthogonal projection of onto a subspace of . ? 3. if is a subspace of and if is in both and , then must be the zero vector. ? 4. the best approximation to by elements of a subspace is given by the vector . ? 5. if an matrix has orthonormal columns, then for all in .