The matrix has rows and columns, so its order is .
Incorrect! Try again.
2Which matrix has all entries equal to zero?
matrices
Easy
A.Scalar matrix
B.Identity matrix
C.Zero matrix
D.Diagonal matrix
Correct Answer: Zero matrix
Explanation:
A zero matrix is a matrix in which every entry is .
Incorrect! Try again.
3What is the transpose of ?
matrices
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The transpose is obtained by interchanging the rows and columns of the matrix.
Incorrect! Try again.
4Which matrix is the identity matrix?
matrices
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
An identity matrix has s on its main diagonal and s elsewhere.
Incorrect! Try again.
5What is the determinant of ?
determinants
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
For a matrix, the determinant is . Thus, .
Incorrect! Try again.
6What is the determinant of the identity matrix ?
determinants
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The determinant of an identity matrix of any order is .
Incorrect! Try again.
7If a square matrix has two identical rows, what is its determinant?
determinants
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
A square matrix with two identical rows has determinant .
Incorrect! Try again.
8A square matrix is invertible when which condition holds?
determinants
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
A square matrix is invertible exactly when its determinant is nonzero.
Incorrect! Try again.
9Which ordered pair solves the system and ?
system of linear equations
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
For , the equations give and .
Incorrect! Try again.
10What does a consistent system of linear equations have?
system of linear equations
Easy
A.Only the zero solution
B.No possible solution
C.Exactly two solutions
D.At least one solution
Correct Answer: At least one solution
Explanation:
A system is consistent when it has at least one solution.
Incorrect! Try again.
11Which matrix form represents the linear system ?
system of linear equations
Easy
A.Variable vector times constant vector equals coefficient matrix
B.Constant matrix plus variable vector equals coefficient vector
C.Coefficient vector minus constant matrix equals variable matrix
D.Coefficient matrix times variable vector equals constant vector
Correct Answer: Coefficient matrix times variable vector equals constant vector
Explanation:
In , contains the coefficients, contains the variables, and contains the constants.
Incorrect! Try again.
12If two equations represent the same straight line, how many solutions does the system have?
system of linear equations
Easy
A.No solutions
B.Infinitely many solutions
C.Exactly two solutions
D.Exactly one solution
Correct Answer: Infinitely many solutions
Explanation:
Every point on the common line satisfies both equations, so there are infinitely many solutions.
Incorrect! Try again.
13If for a nonzero vector , what is called?
eigenvalues
Easy
A.A transpose of
B.A determinant of
C.An inverse of
D.An eigenvalue of
Correct Answer: An eigenvalue of
Explanation:
A scalar satisfying for some nonzero is an eigenvalue of .
Incorrect! Try again.
14What equation is used to find the eigenvalues of a square matrix ?
eigenvalues
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Eigenvalues are the roots of the characteristic equation .
Incorrect! Try again.
15What are the eigenvalues of the diagonal matrix ?
eigenvalues
Easy
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
The eigenvalues of a diagonal matrix are its diagonal entries.
Incorrect! Try again.
16Which vector cannot be an eigenvector?
eigenvectors
Easy
A.A unit vector
B.The zero vector
C.A nonzero vector
D.A column vector
Correct Answer: The zero vector
Explanation:
By definition, an eigenvector must be a nonzero vector.
Incorrect! Try again.
17For , which vector is an eigenvector corresponding to ?
eigenvectors
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Multiplication gives .
Incorrect! Try again.
18If is an eigenvector of with eigenvalue , which equality is true?
eigenvectors
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
An eigenvector satisfies the defining equation .
Incorrect! Try again.
19In LU decomposition, a matrix is written in which form?
LU decomposition
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
LU decomposition expresses as the product of a lower triangular matrix and an upper triangular matrix .
Incorrect! Try again.
20In the factorization , what type of matrix is ?
LU decomposition
Easy
A.Lower triangular matrix
B.Upper triangular matrix
C.Diagonal zero matrix
D.Symmetric identity matrix
Correct Answer: Upper triangular matrix
Explanation:
In LU decomposition, is an upper triangular matrix, so entries below its main diagonal are zero.
Incorrect! Try again.
21Let and . What is ?
matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Using row-by-column multiplication gives .
Incorrect! Try again.
22If , what is ?
matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Here . Substitution gives .
Incorrect! Try again.
23Let and . What is the entry in row , column of ?
matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The required entry is the product of the second row of and the first column of : .
Incorrect! Try again.
24Evaluate .
determinants
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Expanding along the first row gives .
Incorrect! Try again.
25Suppose . Matrix is obtained by interchanging two rows of and then multiplying one row by . What is ?
determinants
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
A row interchange changes the determinant's sign, while multiplying a row by multiplies the determinant by . Thus .
Incorrect! Try again.
26For which values of is the matrix singular?
determinants
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The determinant is . The matrix is singular when this determinant is zero.
Incorrect! Try again.
27If is a matrix with , what is ?
determinants
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
For a matrix, .
Incorrect! Try again.
28Solve the system , , and .
system of linear equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Eliminating gives and . These yield , , and then .
Incorrect! Try again.
29For what value of does the system and have infinitely many solutions?
system of linear equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The second equation must be twice the first equation. Multiplying by gives , so .
Incorrect! Try again.
30A system reduces to and , with free. Which expression describes its solution set?
system of linear equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Set the free variable . Then and , giving .
Incorrect! Try again.
31For which values of does the system and have a unique solution?
system of linear equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The coefficient determinant is . A unique solution exists when it is nonzero, so .
Incorrect! Try again.
32What are the eigenvalues of ?
eigenvalues
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The eigenvalues of a triangular matrix are its diagonal entries. Therefore, they are , , and .
Incorrect! Try again.
33Find the eigenvalues of .
eigenvalues
Medium
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
The characteristic equation is , whose roots are and .
Incorrect! Try again.
34A matrix has eigenvalues , , and . What are the eigenvalues of ?
eigenvalues
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
If is an eigenvalue of , then is an eigenvalue of . Substitution gives , , and .
Incorrect! Try again.
35Which vector is an eigenvector of corresponding to the eigenvalue ?
eigenvectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Solving gives . Thus the eigenspace is spanned by .
Incorrect! Try again.
36Which vector is an eigenvector of corresponding to the eigenvalue ?
eigenvectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Multiplication gives .
Incorrect! Try again.
37For , which matrix diagonalizes as ?
eigenvectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Eigenvectors for and are respectively and . Placing them in the matching column order gives .
Incorrect! Try again.
38Using Doolittle's method, which is the LU decomposition of ?
LU decomposition
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The elimination multiplier is , so the second pivot becomes . These values form and .
Incorrect! Try again.
39Suppose , where and . What is the solution of ?
LU decomposition
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Solving gives . Then gives and , so .
Incorrect! Try again.
40Using Gaussian elimination without row exchanges, what is the lower triangular factor in the LU decomposition of ?
LU decomposition
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The first-column multipliers are and . After the first elimination, the second-column multiplier is .
Incorrect! Try again.
41A real matrix satisfies and . What is ?
matrices
Hard
A.
B.
C.The determinant cannot be determined because the matrix entries and eigenvectors are unspecified.
D.
Correct Answer:
Explanation:
The annihilating polynomial is , so the eigenvalues are and . If has multiplicity , then , giving . Thus .
Incorrect! Try again.
42Let be an invertible matrix with . If column vectors satisfy , find .
determinants
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The matrix determinant lemma gives .
Incorrect! Try again.
43For which values of and does the system
have no solution?
system of linear equations
Hard
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
Subtracting the sum of the first two equations from the third gives . When and , this becomes the contradiction .
Incorrect! Try again.
44A matrix has characteristic polynomial and minimal polynomial . What is ?
eigenvectors
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
For eigenvalue , the algebraic multiplicity is and the largest Jordan block has size . Its blocks must therefore have sizes and , so and the rank is .
Incorrect! Try again.
45For which real values of does
admit an LU decomposition without row exchanges, with all diagonal entries of equal to ?
LU decomposition
Hard
A.
B.
C., because only the second leading principal minor controls the existence of such a decomposition
D.
Correct Answer:
Explanation:
Such an LU decomposition requires all leading principal minors to be nonzero. They are , , and , so cannot be , , or .
Incorrect! Try again.
46Evaluate
determinants
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
This is a Vandermonde determinant for . Its value is .
Incorrect! Try again.
47For a real matrix , which statement about the matrix equation is correct?
matrices
Hard
A.It has a unique solution whenever is invertible.
B.It is solvable precisely when is diagonalizable over the real numbers and has no repeated eigenvalues.
C.It has infinitely many solutions whenever has distinct eigenvalues.
D.It has no solution for any .
Correct Answer: It has no solution for any .
Explanation:
Every commutator has trace zero: . Since over , the equation is impossible.
Incorrect! Try again.
48Consider , where
Which statement is correct?
system of linear equations
Hard
A.For , the system has a unique solution.
B.For every , the system has infinitely many solutions.
C.For , the solution set has dimension .
D.For , the solution set has dimension .
Correct Answer: For , the solution set has dimension .
Explanation:
Writing gives , so . Thus consistency requires . Since , the solution set then has dimension .
Incorrect! Try again.
49Let be an invertible real matrix satisfying . Which value cannot equal ?
eigenvalues
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Invertibility and imply , so every eigenvalue is or . The trace is the sum of five such values and must therefore be odd, so it cannot be .
Incorrect! Try again.
50Let . Which vector is an eigenvector of but not an eigenvector of ?
eigenvectors
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , is an eigenvector of with eigenvalue . But , which is not a scalar multiple of it.
Incorrect! Try again.
51Using Doolittle factorization , where has unit diagonal, let
What is the ordered pair ?
LU decomposition
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Elimination gives multipliers , , and . The final pivot is , so the pair is .
Incorrect! Try again.
52Let be a real skew-symmetric matrix with . What is ?
determinants
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
For an matrix of rank , the adjugate has rank . Here , so .
Incorrect! Try again.
53Let be a matrix of rank with and . If and is one solution of , what is the complete solution set?
system of linear equations
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The condition ensures consistency because spans the left nullspace. Every two solutions differ by an element of , giving .
Incorrect! Try again.
54A matrix has eigenvalues , , and . Find
eigenvalues
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The transformed eigenvalues are . For , these are , , and , whose product is .
Incorrect! Try again.
55Suppose is an complex matrix with distinct eigenvalues and . Which conclusion must hold?
eigenvectors
Hard
A.Every eigenvector of is an eigenvector of .
B. must be a polynomial in of degree exactly , with a nonzero leading coefficient.
C. and must have exactly the same distinct eigenvalues.
D.Every eigenvector of is an eigenvector of .
Correct Answer: Every eigenvector of is an eigenvector of .
Explanation:
If , then . Thus lies in the one-dimensional -eigenspace of , so is a scalar multiple of .
Incorrect! Try again.
56If and are matrices with , what is the smallest possible value of ?
matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Sylvester's rank inequality gives . This bound is attainable by choosing to intersect in dimension .
Incorrect! Try again.
57For an arbitrary matrix , evaluate the block determinant
determinants
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Interchanging the two groups of three block columns contributes and produces the block upper-triangular matrix , whose determinant is . Hence the original determinant is .
Incorrect! Try again.
58Let be the tridiagonal matrix with every diagonal entry equal to and every entry immediately above or below the diagonal equal to . In the Doolittle factorization , what is ?
LU decomposition
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The pivots satisfy and . This yields , so .
Incorrect! Try again.
59Let be invertible and let nonzero vectors satisfy . For the system , which statement is correct?
system of linear equations
Hard
A.It is solvable exactly when , and then it has a unique solution.
B.It is solvable exactly when , and then it has a one-parameter family of solutions.
C.It has a unique solution for every because adding a rank-one matrix to an invertible matrix preserves invertibility.
D.It is solvable exactly when , and then it has a one-parameter family of solutions.
Correct Answer: It is solvable exactly when , and then it has a one-parameter family of solutions.
Explanation:
The condition makes singular with nullity . Its left nullspace is spanned by , so consistency requires ; a consistent system then has one free parameter.
Incorrect! Try again.
60A matrix satisfies , , and . What is the spectral radius of ?
eigenvalues
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The second elementary symmetric sum is , so the characteristic polynomial is . The eigenvalues of are , , and , giving spectral radius .
Incorrect! Try again.
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