Problem 1 [10 pts.] (a) [1 pt.] Correct answer: true [2 pts.] Justification Okay if case of zero ideal is not mentioned Mention that any nonzero polynomial in I with minimal degree is a generator Use the division algorithm to justify the above claim (b) [1 pt.] Correct answer: false [1 pt.] Justification (c) [1 pt.] Correct answer: true [2 pts.] Justification k[x]/(q(x)) is a field k[x]/(q(x)) has dim 5 as vector space over k (d) [1 pt.] Correct answer: true [1 pt.] Justification Problem 2 [3 pts.] [1 pt.] Correct answer: false [1 pt.] Correct setup: k,L,W,subset chosen appropriately [1 pt.] Correct justification Problem 3 [7 pts.] Let S={v_1,...,v_n} and W the subspace of V spanned by S [1 pt.] Stating (c) = (a) + (b) [3 pts.] (a) --> (b) [3 pts.] (b) --> (a) Problem 4 [6 pts.] Let S be a subset of V with m>n elements Method 1: Assume for the sake of contradiction that S is linearly independent Use Problem 3 to argue that W:=Span(S) has dim m Use Homework 1 Problem 2 to show W \iso k^r for some r \leq n Derive a contradiction using Homework 1 Problem 4(a) (uniqueness of dim) Method 2: Choose S' a maximal linearly independent subset of S Use Problem 5 to argue that S' has size at most n Deduce that S is linearly dependent Method 3: Show that any linearly independent subset of V can be extended to a basis Problem 5 [12 pts.] (a) [1 pt.] Mention that {v,T(v),...,T^n(v)} has n+1 elements [1 pt.] Find a linear dependence relation (b) [1 pt.] Show that p(T) commutes with vector addition [1 pt.] Show that p(T) commutes with scalar multiplication (c) [1 pt.] Correct use of convolution [1 pt.] Show work (d) [1 pt.] Pick a basis {v_1,...,v_n} of V [1 pt.] Use (a) for each i to find a nonzero p_i(x) in k[x] such that p_i(T)(v_i)=0 [1 pt.] Invoke p(x):=p_1(x)...p_n(x) [2 pts.] Show that p(x) satisfies p(T)=0 Use that p_i(T)(v_i)=0 Note that p_i(T) and p_j(T) commute [1 pt.] Explain why p(x) is nonzero in k[x] Problem 6 [2 pts.] Use Problem 5(d) to choose p(x) in C[x] nonzero (monic) of minimal degree such that p(T)=0 [2 pts.] Use fundamental theorem of algebra to write p(x)=(x-\lambda)q(x) for some \lambda in C [2 pts.] Argue that q(T) \neq 0 for degree reasons and so q(T)(v) \neq 0 for some v in V [2 pts.] Show that \lambda is eigenvalue of T with eigenvector q(T)(v) Problem 7 [3 pts.] Write f(x) in terms of coefficients Find the images of 1,...,x^{d-2} mod f(x) Find the image of x^{d-1} mod f(x) Write everything in matrix form Problem 8 [8 pts.] Problem 9 [8 pts.] Let A be the matrix 0 -1 1 0 Show that A is diagonalizable over C [2 pts.] Show that A has eigenvalues i and -i [2 pts.] Show that A has two linearly independent eigenvectors [2 pts.] Relate diagonalizability to existence of an eigenbasis Show that A is not diagonalizable over R [1 pt.] Mention that a 2x2 matrix must have all real eigenvalues to be diagonalizable over R [1 pt.] Explain why the above is true