The Linear Logo

Dr. Mark V. Sapir


Class 23

Exercises


Homework due Class 24.

  1. Is it true that the set of all continuous functions f(x) on [0,1] with f(1/2)=1 is a subspace of C[0,1]?
  2. Is it true that the set of all n by n matrices A with trace(A)=0 is a subspace of the vector space of all n by n matrices?
  3. Is it true that the map which takes every function f(x) from C[0,1] to the number f(1) is a linear transformation from C[0,1] to R?
  4. Is it true that the map which takes every function f(x) from C[0,1] to the integral from 0 to 1 of f(x) is a linear transformation from C[0,1] to R.

"Proof" homework due Class 26

  1. Proof the theorem about linear transformations of arbitrary vector spaces.

Solutions

Maple HTML

Index Concepts Cover Page

Class 24

Exercises


Homework due Class 25.

Find the kernel and range of the following linear transformations:

  1. The transformation from C[0,1] to R which takes every function f(x) to the number f(1).
  2. The operator on the space of 2 by 2 matrices to itself which takes every matrix

    [ a b ]
    [ c d ]


    to the product

      
                              [1 2]   [a b]
                              [   ] * [   ]
                              [0 1]   [c d]
    


    (Hint: use the fact that the matrix

    [ 1 2 ]
    [ 0 1 ]

    is invertible.).

In these problems, you do not have to prove that the maps are in fact linear transformations.


Index Concepts Cover Page

Class 25

Exercises


Bonus problems. Due Class 33

  1. (5 points). Prove every rotation in R2 is a product of two reflections.
  2. (7 points).Suppose that T is a linear operator in the Euclidean vector space V. Assume that T preserves lengths of vectors that is for every vector v the length of T(v) coincides with the length of v. Prove that T preserves dot products that is for every two vectors u and v the dot product <u,v > is equal to the dot product of T(u) and T(v).
  3. (5 points). Prove or disprove that every linear operator in R2 which preserves lengths is a product of several reflections about lines.
  4. (7 points). Prove or disprove that every linear operator in R3 which preserves lengths is a product of several reflections about planes in R3.

Solutions

Maple HTML

Index Concepts Cover Page

Class 26

Exercises


Homework due Class 27.

  1. Check if the vector (1,2,3,4) belongs to the column space of the matrix

    [ 1 2 3 ]
    [ 4 5 6 ]
    [ 7 8 9 ]
    [ 0 1 2 ]

  2. Find the null space of the matrix

    [ 1 2 3 4 5 ]
    [ 2 3 4 5 6 ]
    [ 1 0 2 0 6 ]

  3. Let p1=x3+x+1, p2=2x3-x2, p3=x2+x+1, q1=x3-1, q2=x3-x2+1, q3=x3+x be polynomials. Is it true that span{p1,p2,p3}=span{q1,q2,q3}?
  4. Find the kernel of the linear transformation from R4 to R2 with the following standard matrix:

    [ 1 2 3 4 ]
    [ 2 1 3 4 ]

  5. Is it true that the range of the transformation in the previous problem coincides with R2?

Solutions

HTML

Index Concepts Cover Page

Class 27

Exercises


Homework due Class 28.

  1. Check whether the following vectors in R5 are linearly independent. If they are not linearly independent, find one of them which is a linear combinationof the others.
    1. (1,2, 3, 4, 5), (2,3,4,5,6), (1,0,0,0,1), (2, 5, 7, 9, 10);
    2. (2,1,1,1,1), (2,1,4,4,4), (3,3,3,1,1).
  2. Are these functions linearly independent as elements of C[0,1]: f(x)=x, g(x)=ex, h(x) = e2x.

Solutions

Maple HTML

Index Concepts Cover Page

Class 28


Solutions

Maple HTML

Index Concepts Cover Page

Test 2


Solutions

Maple HTML

Index Concepts Cover Page

Class 29


Exercises

Homework due Class 30.

  1. For which real values of t the following vectors form a linearly independent set in R4:
    (t, 2t, 3 4), (1, 2, 3t, 4t), (t, 2, 3t, 4), (t, 2, 3, 4t).
  2. Show that the following set of functions from C[0,1] is linearly independent: x, xex, x2ex, x3ex.

"Proof" homework due Class 31

Prove that

  1. If a subset S of a vector space V contains 0 then S is linearly dependent.
  2. A set S with exactly two vectors is linearly dependent if and only if one of these vectors is a scalar multiple of the other.
  3. If a subset of a set S is linearly dependent then the whole set is linearly dependent

Class 30

Solutions

Maple HTML

Index Concepts Cover Page

Class 31


Exercises

Computational homework due Class 32

  1. For which values of t the following 4-vectors form a basis of R4: (1,t,3,4), (t, t, 3, 4t), (1,t, 3t, 4), (1, 1, 3, 4t) ?
  2. Find a basis in R4 containing the following vectors: (1,1,2,2), (2,3,3,3).
  3. Find a basis of R3 contained in the following set of vectors: (1, 1, 1), (2, 2, 2), (3, 3, 3), (1, 2, 3), (2, 3, 4), (3, 2, 1).
  4. What is the dimension of the subspace of R4 spanned by the vectors (1,2,3,4), (1,1,1,1), (3, 4, 5, 6), (5, 7, 9, 11)?

"Proof" homework due Class 34

  1. Prove that if vectors v1,...,vn span a vector space V then the vectors v1-v2, v2-v3, ..., vn-1-vn, vn span V.
  2. Prove that if V is a subspace of a vector space W then dim(V) does not exceed dim(W).
  3. Prove that if V is a subspace of W, dim(V)=dim(W) and W is finite dimensional then V=W.
  4. Let Pn be the space of polynomials of degree at most n. Prove that for every number a the set {1, (x-a), (x-a)2,...,(x-a)n} is a basis of Pn and the coordinates of every polynomial f(x) from Pn in this basis are (f(a), f'(a), 1/2 f''(a), 1/6 f'''(a),..., (1/(n!)) f(n) (a) ).

Bonus Problems
  1. (5 points) Let a1, a2,..., ak be a linearly independent system of vectors in a vector space V. Find all bases contained in the following system of vectors: b1=a1-a2, b2=a2-a3,...,bk-1=ak-1-ak, bk=ak-a1.
  2. (5 points) In which case a system of vectors spanning a vector space V has a unique subsystem which is a basis of V?
  3. (7 points) Let A be a n by n matrix. Suppose that for every i=1,...,n the absolute value of the diagonal entry A[i,i] is bigger than the sum of absolute values of other entries in the same row. Prove that the column vectorsof this matrix are linearly independent.

Solutions

Maple HTML

Index Concepts Cover Page

Class 32

Exercises


Computational homework due Class 33

  1. Find the rank of the set of vectors in R5 usng only the definition of the rank: (1,2,3,4,5), (6,7,8,9,10), (1,1,1,1,1), (2,2,2,2,2), (5,4,3,2,1), (6,5,4,3,2).
  2. Find the row rank and the column rank of the following matrix using only the definition of the rank:

    [ 2 3 4 5 6 ]
    [ 1 1 1 1 1 ]
    [ 0 0 0 2 3 ]

  3. Find the rank of the following set of polynomials: x3+x2+x, x3+x+1, x3+x2+x, 2x3+x2+x+1.

Solutions

HTML

Index Concepts Cover Page

Class 33


Solutions

HTML

Index Concepts Cover Page

Class 34


Solutions

Maple HTML

Index Concepts Cover Page

Class 35


Exercises

Computational homework due Class 36

  1. Find the basis of the orthogonal complement of the subspace of R4 spanned by the vectors (1,2,3,4) and (2,3,1,1).
  2. For which values of t the following matrices form a basis in M2,2:
    [ t 2t ]
    [ 2 3t ]
    [ 1 2 ]
    [ 2t 3 ]
    [ 1 2t ]
    [ t+1 t+2 ]
    [ 1 t+1 ]
    [ 2 2t+1 ]

"Proof" homework due Class 37

  1. Let {v1,...,vn} be a basis of a vector space V. Let s1,...,sm be vectors of V and we have that

    s1=a11 v1 +...+ a1n vn
    s2=a21 v1 +...+ a2n vn
    ............................
    sm=am1 v1 +...+ amn vn

    for some numbers aij. Consider the following n-vectors:

    t1 = (a11, ..., a1n)
    t2 = (a21, ..., a2n)
    ..........................
    tm = (am1, ..., amn)

    Prove that the set {s1,...,sm} is linearly independent if and only if the set {t1,...,tm} is linearly independent.

Solutions


Index Concepts Cover Page

Class 36


Solutions

Maple HTML

Index Concepts Cover Page

Class 37


Exercises

Homework due Class 38.

  1. Find an orthogonal basis of the subspace of C[0,1] spanned by the functions sin(x), cos(x), x.
  2. Find the distance from the function ex to the subspace spanned by the functions sin(x), cos(x), x in C[0,1].

Solutions

HTML

Index Concepts Cover Page

Class 38


Exercises

Homework due Class 39.

  1. Let A be the following matrix:

    [ 1 2 3 ]
    [ 3 4 5 ]
    [ 2 1 3 ]
    [ 3 3 6 ]
    [ 4 6 8 ]

    Find a vector v=(x,y,z) which makes Av closest to the vector (1,2,3,4,5).


Solutions

HTML

Index Concepts Cover Page

Class 39


Solutions

Maple HTML

Index Concepts Cover Page

Test 3


Solutions

HTML

Index Concepts Cover Page

Class 40

Exercises


Problems about eigenvectors and eigenvalues

  1. "Proof" problems.
    1. Let v and w be eigenvectors of a linear operator T which correspond to different eigenvalues a and b. Prove that v and w are not proportional.
    2. Let v1, ..., vk be eigenvectors of T corresponding to pairwise different eigenvalues a1,...,ak. Prove that v1,...,vk are linearly independent (if you cannot solve this problem, see the book, chapter 7).
    3. Prove that the characteristic polynomials of two similar matrices are equal.
    4. Let A be a square matrix such that An=0 for some n. Prove that all eigenvalues of A are equal to 0 (use the definition of an eigenvalue).
    5. Prove that A and AT have the same eigenvalues (here A is a square matrix).
    6. Prove that if a matrix A is similar to a diagonal matrix then A2 is also similar to a diagonal matrix.
    7. Prove that if two matrix are similar and one of them is invertible then the other one is invertible too.
    8. Prove that similar matrices have the same determinants.
    9. Prove that similar matrices have the same traces.
    10. (Bonus, 10 points). Prove that if A is a symmetric matrix then eigenvectors corresponding to different eigenvalues are orthogonal.
    11. (Bonus, 20 points). Prove that if the standard matrix A of a linear operator T in Rn is symmetri then T has a basis of eigenvectors.
    12. (Bonus, 7 points). Prove that an upper triangular matrix A is similar to a diagonal matrix if and only if A is diagonal.
  2. Computational problems
    1. Let V be the space of all polynomials of degree at most 3. Let T be the linear operator in V which takes each polynomial to its derivative. Find eigenvalues and eigenvectors of this operator.
    2. Let T be the linear operator in R2 with the following standard matrix:

      [ 2 2 ]
      [ 8 2 ]


      Find the basis where this operator has a diagonal matrix.

    3. Find all eigenvectors and eigenvalues of the following matrix:

      [ 4 0 1 ]
      [ 2 3 2 ]
      [ 1 0 4 ]

      solution.

    4. Determine whether the linear operator in Rn with the following standard matrix:

      [ 3 0 2 ]
      [ 0 2 0 ]
      [ 0 1 2 ]

      has a basis of eigenvectors. Hint: find the eigenvalues of this matrix; look how many lineraly independent eigenvectors correspond to each eigenvalue (find the general solution of the corresponding system of equations); find out if the total number of the linearly independent vectors corresponding to all the eigenvalues is equal to the dimension of R3.

    5. Determine whether the following matrix is similar to a diagonal matrix.

      [ 1 0 0 ]
      [ 1 1 0 ]
      [ 1 1 1 ]

Solutions


Index Concepts Cover Page

The Final Test. Spring 96.


To see the test, click here.

The Final Test. Fall 96.


To see the test, click here. To see the solutions, click here.
Submit Homework