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MATH2001/7000 ASSIGNMENT
Due at 5:00pm 8 September. Marks for each question are shown. Total marks: 25 Submit your assignment online via the assignment 2 Gradescope submission link in Black- board. (1) (6 marks.) Let C[0, 1] have the inner product defined by 〈f ,g〉 = ∫ 1 0 f(x)g(x)dx, ∀f ,g ∈ C[0, 1]. Let U = span{x− 1, x+ 1, x+ x2} be a subspace of C[0, 1]. Find the best (i.e. least squares) approximation of cosh(x) in the subspace U . (2) (5 marks.) Let A = 4 2 20 4 0 0 −2 2 . (a) Find the eigenvalues and eigenvectors of A. (b) Compute An, where n ≥ 1 is an integer. (3) (5 marks.) Let A be a 3 × 3 real symmetric matrix and have eigenvalues λ1 = 2, λ2 = λ3 = 1. The eigenvectors corresponding to λ2 = λ3 = 1 are respectively given by v2 = 10 1 , v3 = 12 −1 . Find the eigenvector of A corresponding to λ1 = 2 and the matrix A. (4) (6 marks.) Let A = 3 2 42 0 2 4 2 3 . You are given that the characteristic equation of A is (λ+ 1)2(λ− 8) = 0, i.e. the eigenvalues of A are λ = −1, 8. (a) Find the eigenvectors of A. (b) Are the eigenvectors of A corresponding to the eigenvalue λ = −1 orthogonal with respect to the usual dot product? If not, apply the Gram-Schmidt process to turn them into an orthonormal set of eigenvectors. (c) Find an orthogonal matrix P that orthogonally diagonalizes A. 1 (5) (3 marks.) Let f(x, y, z) = x2 + y2 + z2 + 4b yz be a quadratic form, where b ∈ R. Suppose that after the variable change, xy z = P uv w , where P is an orthogonal matrix, the quadratic form becomes f = u2 + 2v2 in terms of the new variables u, v and w. Determine all possible values for b.