Math 2568 Summer 2022 Final Exam
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
Math 2568 Summer 2022
Final Exam
Problem 1 Let A = ┌ ┐
'13 9 10 _6 8 '.
a) [4 pts] Find a basis for N(A) in rational format.
b) [3 pts] Find a particular solution to the matrix equation A * x = ┌ 5_2┐
14
c) [3 pts] Use your answers in a), b) and the Superposition Principle to express the general solution in vector form to the matrix equation in b).
Problem 2 [10 pts] For a fixed matrices B, C ∈ R2×2, let W = eA ∈ R2×2 I A * B = 2A * C}. Determine if W is a subspace of R2×2 (either prove that it is, or show via specific counterexample that it isn’t).
Problem 3 Let L : R4 → R3 be given by L ╱(( ┌'''┐'''、ìì = '(┌)(_x4 )'(┐) .
a) [4 pts] Show that L is a linear transformation, and find the matrix representation A of L with respect to the standard bases for R4 and R3 .
b) [3 pts] Use part a) to find a basis for ker(L).
c) [3 pts] Use part a) for find a basis for im(L).
Problem 4 A set of vectors is given by S = ev1 , v2 , v3 } in R3 where
ev1 = '(┌)5_74'(┐) , ev2 = '(┌)'(┐) , ev3 = '(┌)1_1'(┐)
a) [3 pts] Show that S is a basis for R3 .
b) [4 pts] Using the above coordinate vectors, find the base transition matrix eTS from the basis S to the standard basis e. Then compute the base transition matrix STe from the standard basis e to the basis S .
c) [3 pts] If ev = '(┌)'(┐), compute S v (the coordinate vector of v with respect to the basis S). Use this to express v as a linear combination of the vectors in S .
Problem 5 Six data points are given by (_4, 2), (_1, 5), (0, 10), (2, 7), (6, 13), and (8, 9).
a) [3 pts] Find the least-squares fit by a linear function.
b) [3 pts] Find the least-squares fit by a quadratic function.
b) [4 pts] Find the smallest degree polynomial which fits the points exactly.
Problem 6 A bilinear pairing on R2 is given on basis vectors by
< e1 , e1 >= 13; < e1 , e2 >=< e2 , e1 >= 7; < e2 , e2 >= 26
a) [3 pts] Find the matrix representation of the pairing.
b) [4 pts] Explain why the bilinear pairing defines an inner product.
c) [3 pts] If v = [5 _ 3]T , find a non-zero vector w with < v, w >= 0
┌ 5(4) Problem 7 Let A = '(') _1 ' 3 |
5 0 2 1 2 |
_1 2 9 _4 1 |
3 1 _4 2 0 |
2(7) ┐ 1 '(') 0 ' |
a) [4 pts] Using the [V, D] command in MATLAB with rational format, find a diagonal matrix D and a matrix V of maximal rank satisfying the matrix equation A * V = V * D . Is A real-diagonalizable?
b) [4 pts] Write down the eigenvalues of A. For each eigenvalue, find a basis for the corresponding eigenspace of A.
c) [4 pts] Define a pairing on R5 by < v, w >= vT * A * w. Show that this pairing is a bilinear symmetric pairing on R5 . Is the pairing an inner product? (you should justify your answer either way)
Problem 8 Let P4 be the space of polynomials of degree less than 4 with real coefficients. Define L : P4 → P4 by
L(p(x)) = 5x2p\\\ (x) _ (3x + 2)p\\ (x) + 7p\ (x)
a) [5 pts] Find the matrix representing L with respect to the standard basis S = e1, x, x2 , x3 } of P4 . Explain how this can be used to prove directly that L is a linear transformation.
b) [4 pts] Let S\ = e(4 + 3x), (2 _ x3 ), (1 + 5x _ x2 ), (x + x3 )}. Show that S\ is a basis for P4 .
c) [4 pts] Compute the base transition matrix S\TS .
d) [3 pts] Use a) and c) to compute S\LS\, the matrix representative of L with respect to the basis S\ .
┌ 4(3) ┐ ┌ 2_1┐ ┌ 7_2┐ ┌ 1(_)0(4)┐
Problem 9 Let u1 = '(') _2'('), u2 = '(') 0 '('), u3 = '(') 9 '(') . Also let v = '(') _6'(') .
' 5 ' ' 5 ' ' 1 ' ' 0 '
a) [4 pts] Compute prW (v) where W = Spaneu1 , u2 , u3 } c R5 .
b) [4 pts] Compute prW/ (v) where WL denotes the orthogonal complement of W in R5 .
c) [3 pts] Compute the distance between v and W .
┌ 1(5) ┐ ┌ 3_2┐ ┌ _03┐
a) [6 pts] Use the Gram-Schmit algorithm to find an orthogonal basis for W . You should explicitly show each step of your calculation.
┌ 1_7(0)┐
' 11 '
b) [5 pts] Let v = 4 Compute the projection prW (v) of v onto the subspace W using the
'_1 '
orthogonal basis in a).
c) [4 pts] Use the computation in b) to compute the distance between v and W .
┌ ┐
Problem 11 Let A = '''.
a) [3 pts] Compute the characteristic polynomial of A and find its roots.
b) [4 pts] For each eigenvalue of A find a basis for the corresponding eigenspace.
c) [3 pts] Determine if A is defective. Justify your answer.
d) [6 pts] If A is defective, determine the defective eigenvalue or eigenvalues, and find a Jordan chain (or set of Jordan chains) in the corresponding generalized eigenspace that provides a canonical basis for that space.
Problem 12 Let B be the matrix given by
A = ┌a(4) b(0)
'b (a + b)
where a and b are indeterminates.
_a2┐
2b'
a) [6 pts] Using row operations that exist for all values of a or b, together with cofactor expansion, compute the determinant of A expressed as a function of a and b.
b) [4 pts] Use this to determine a relation between a and b that provides necessary and sufficient conditions for the matrix A to be singular (your relation should be an equation involving a and b).
For the following six questions, indicate whether the following statements are true or false. In each case give a reason for your answer.
Problem 13 [10 pts] If L : V → W is a linear transformation of vector spaces and U c W is a subspace of W , then ev ∈ V I L(v) ∈ U} c V is a subspace of V .
Problem 14 [10 pts] The set eA ∈ R2×2 I A is nonsingular} is a subspace of R2×2 .
Problem 15 [10 pts] If A, B are two n × n matrices, then A is similar to B if and only if pA (t) = pB (t).
Problem 16 [10 pts] For an n × n matrix A, pA (t) = t . q(t) for some polynomial q(t) precisely when Det(A) = 0.
Problem 17 [10 pts] If W c Rn is a subspace and v ∈ Rn , then prW (v) is the least-squares approximation to v by a vector in W except when prW (v) = 0.
Problem 18 [10 pts] If A is a real n × n matrix, then the pairing defined by < v, w >:= vT * AT * A * w
is an inner product on Rn if and only if A is invertible.
2022-08-02