1. True or false: (a) if E is a subspace of V, then dim(E) + dim(E+) = dim(V) (b) Let {i, n} be a basis of the vector space V, where vi,..., are all eigen- vectors for both the matrix A and the matrix B. Then, any eigenvector of A is an eigenvector of B. Justify. 2. Apply Gram-Schmidt orthogonalization to the system of vectors {(1, 2, -2), (1, −1, 4), (2, 1, 1)}. 3. Suppose P is the orthogonal projection onto a subspace E, and Q is the orthogonal projection onto the orthogonal complement E. (a) The combinations of projections P+Q and PQ correspond to well-known oper- ators. What are they? Justify your answer. (b) Show that P - Q is its own inverse. 4. Show that the Frobenius product on n x n-matrices, (A, B) = = Tr(B*A), is an inner product, where B* denotes the Hermitian adjoint of B. 5. Show that if A and B are two n x n-matrices for which {1,..., n} is a basis of eigen- vectors (for both A and B), then AB = BA. Remark: It is also true that if AB = BA, then there exists a common…

Question 1. Let f: XY and g: Y Z be two functions. Prove that (1) if go f is injective, then f is injective; (2) if go f is surjective, then g is surjective. Question 2. Prove or disprove: (1) The set X = {k € Z} is countable. (2) The set X = {k EZ,nЄN} is countable. (3) The set X = R\Q = {x ER2 countable. Q} (the set of all irrational numbers) is (4) The set X = {p.√2pQ} is countable. (5) The interval X = [0,1] is countable. Question 3. Let X = {f|f: N→ N}, the set of all functions from N to N. Prove that X is uncountable. Extra practice (not to be submitted). Question. Prove the following by induction. (1) For any nЄN, 1+3+5++2n-1 n². (2) For any nЄ N, 1+2+3++ n = n(n+1). Question. Write explicitly a function f: Nx N N which is bijective.

3. Suppose P is the orthogonal projection onto a subspace E, and Q is the orthogonal projection onto the orthogonal complement E. (a) The combinations of projections P+Q and PQ correspond to well-known oper- ators. What are they? Justify your answer. (b) Show that P - Q is its own inverse.