1How many rows and columns does a matrix of order have?
review of matrices
Easy
A.3 rows and 2 columns
B.2 rows and 2 columns
C.2 rows and 3 columns
D.3 rows and 3 columns
Correct Answer: 2 rows and 3 columns
Explanation:
In the order , denotes the number of rows and denotes the number of columns.
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2Which matrix has all diagonal entries equal to and all other entries equal to ?
review of matrices
Easy
A.Scalar matrix
B.Zero matrix
C.Triangular matrix
D.Identity matrix
Correct Answer: Identity matrix
Explanation:
An identity matrix has on its main diagonal and everywhere else.
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3Which notation represents the interchange of the first and second rows?
elementary operations of matrices
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The symbol indicates that the two rows are interchanged.
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4Which of the following is a valid elementary row operation?
elementary operations of matrices
Easy
A.Multiplying a row by
B.Adding a new row
C.Multiplying a row by
D.Deleting a row
Correct Answer: Multiplying a row by
Explanation:
A row may be multiplied by any nonzero scalar as an elementary row operation.
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5The rank of a matrix is equal to the maximum number of what kind of rows or columns?
rank of a matrix
Easy
A.Nonzero rows or columns
B.Linearly independent rows or columns
C.Linearly dependent rows or columns
D.Equal rows or columns
Correct Answer: Linearly independent rows or columns
Explanation:
Rank is the maximum number of linearly independent rows or columns in a matrix.
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6What is the rank of the identity matrix ?
rank of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
All three rows of are linearly independent, so its rank is .
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7A set of vectors is linearly dependent if one vector can be expressed as what?
linear dependence and independence of vectors
Easy
A.A linear combination of the others
B.A scalar quantity
C.A product of the others
D.A zero determinant
Correct Answer: A linear combination of the others
Explanation:
Linear dependence means that at least one vector is a linear combination of the remaining vectors.
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8Which pair of vectors in is linearly independent?
linear dependence and independence of vectors
Easy
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
Neither nor is a scalar multiple of the other, so they are linearly independent.
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9A linear system is consistent when it has what?
solution of linear system of equations
Easy
A.No possible solution
B.Exactly two solutions
C.At least one solution
D.Only the zero solution
Correct Answer: At least one solution
Explanation:
A consistent system is a system that has one or more solutions.
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10What is the solution of the system and ?
solution of linear system of equations
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Adding the equations gives , so ; substituting gives .
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11If is an invertible square matrix, how many solutions does have for every ?
solution of linear system of equations
Easy
A.Exactly two solutions
B.No solutions
C.Exactly one solution
D.Infinitely many solutions
Correct Answer: Exactly one solution
Explanation:
When is invertible, the unique solution is .
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12For an invertible matrix , which equation defines its inverse ?
inverse of matrices
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The product of an invertible matrix and its inverse is the identity matrix.
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13What is the inverse of the diagonal matrix ?
inverse of matrices
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The inverse of a diagonal matrix is obtained by taking the reciprocal of each nonzero diagonal entry.
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14If satisfies , what is called?
eigenvalues and eigenvectors
Easy
A.An eigenvalue
B.A matrix rank
C.A row vector
D.A determinant
Correct Answer: An eigenvalue
Explanation:
A scalar satisfying for a nonzero vector is an eigenvalue of .
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15For , which vector is an eigenvector corresponding to the eigenvalue ?
eigenvalues and eigenvectors
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Multiplication gives .
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16The sum of the eigenvalues of a square matrix, counting multiplicities, equals which quantity?
properties of eigenvalues
Easy
A.The trace of the matrix
B.The order of the matrix
C.The rank of the matrix
D.The norm of the matrix
Correct Answer: The trace of the matrix
Explanation:
The sum of all eigenvalues, including multiplicities, equals the trace of the matrix.
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17The product of the eigenvalues of a square matrix, counting multiplicities, equals which quantity?
properties of eigenvalues
Easy
A.Its rank
B.Its determinant
C.Its trace
D.Its dimension
Correct Answer: Its determinant
Explanation:
The determinant of a square matrix equals the product of its eigenvalues, counting multiplicities.
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18If is an eigenvalue of , what is the corresponding eigenvalue of ?
properties of eigenvalues
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
From , it follows that .
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19What does the Cayley-Hamilton theorem state about a square matrix ?
Cayley-Hamilton theorem
Easy
A. satisfies its characteristic equation
B. always has distinct eigenvalues
C. always has an inverse
D. equals its transpose
Correct Answer: satisfies its characteristic equation
Explanation:
The Cayley-Hamilton theorem states that every square matrix satisfies its own characteristic equation.
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20If the characteristic polynomial of is , which equation follows from the Cayley-Hamilton theorem?
Cayley-Hamilton theorem
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Substituting for in the characteristic polynomial gives .
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21If and , what is ?
review of matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Using row-by-column multiplication gives .
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22For , the operation produces a matrix . What is ?
elementary operations of matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Adding a multiple of one row to another does not change the determinant. Thus .
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23What is the rank of ?
rank of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The second row is twice the first, while the third row is independent of the first. Therefore, there are two linearly independent rows.
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24For what value of does have rank ?
rank of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
A nonzero matrix has rank when its determinant is zero. Here, , so .
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25Which set of vectors is linearly dependent?
linear dependence and independence of vectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The second vector is twice the first, so the set contains a nontrivial linear relation and is linearly dependent.
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26For which values of are the vectors , , and linearly independent?
linear dependence and independence of vectors
Medium
A.
B. only
C. only
D.
Correct Answer:
Explanation:
Placing the vectors as columns gives a determinant of . The vectors are independent exactly when this determinant is nonzero.
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27Solve the system and .
solution of linear system of equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Adding the equations gives , so . Substitution into gives .
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28For what value of does the system and have infinitely many solutions?
solution of linear system of equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The second equation must be twice the first. Multiplying by gives , so .
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29Find the solution of , , and .
solution of linear system of equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Subtracting the second equation from the first gives . The remaining equations then yield and , giving and .
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30A homogeneous system has unknowns and a coefficient matrix of rank . Which statement describes its solution set?
solution of linear system of equations
Medium
A.It has one free parameter.
B.It has two free parameters.
C.It has a unique nonzero solution.
D.It has no solution.
Correct Answer: It has one free parameter.
Explanation:
The nullity is by the rank-nullity relation. Hence the homogeneous system has infinitely many solutions described by one free parameter.
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31What is the inverse of ?
inverse of matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , the inverse is .
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32If and , what is ?
inverse of matrices
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The equation implies . Since , applying the inverse formula gives the stated matrix.
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33What are the eigenvalues of ?
eigenvalues and eigenvectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The eigenvalues of a triangular matrix are its diagonal entries. Therefore, they are , , and .
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34Which vector spans the eigenspace of corresponding to ?
eigenvalues and eigenvectors
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Solving gives , while is free. Thus the eigenspace is spanned by .
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35What are the eigenvalues of ?
eigenvalues and eigenvectors
Medium
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
The characteristic polynomial is , so the eigenvalues are and .
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36A matrix has trace and determinant . If two eigenvalues are and , what is the third eigenvalue?
properties of eigenvalues
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The trace equals the sum of the eigenvalues. Thus , giving , which also makes their product .
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37If the eigenvalues of an invertible matrix are and , what are the eigenvalues of ?
properties of eigenvalues
Medium
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
The eigenvalues of are the reciprocals of the eigenvalues of . Therefore, they are and .
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38If is an eigenvalue of , what is the corresponding eigenvalue of ?
properties of eigenvalues
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
If , then . For , the corresponding eigenvalue is .
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39Which matrix equation follows from the Cayley-Hamilton theorem for ?
Cayley-Hamilton theorem
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The characteristic polynomial is . By the Cayley-Hamilton theorem, .
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40An invertible matrix satisfies . Which expression equals ?
Cayley-Hamilton theorem
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Multiplying by gives . Hence .
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41Let be matrices, with invertible. If and what is the determinant of the block matrix ?
review of matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The Schur-complement formula gives . Since the second determinant is , the result is .
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42A matrix has . Matrix is obtained by successively applying , , , and . What is ?
elementary operations of matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The swap contributes , the row scaling contributes , the column replacement contributes , and the final scaling contributes . Thus .
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43For which statement correctly describes its rank?
rank of a matrix
Hard
A. for and otherwise
B. for and otherwise
C. only for and otherwise
D. only for and otherwise
Correct Answer: for and otherwise
Explanation:
The determinant is , so the rank is unless or . At either exceptional value, a nonzero minor remains, giving rank .
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44Let , , and . Which statement is correct?
linear dependence and independence of vectors
Hard
A.The vectors are independent exactly when
B.The vectors are independent exactly when
C.The vectors are dependent for every real
D.The vectors are dependent exactly when
Correct Answer: The vectors are independent exactly when
Explanation:
Using the vectors as columns gives determinant . It is nonzero exactly when ; at , the relation is .
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45Consider Which classification is correct?
solution of linear system of equations
Hard
A.Unique for every except ; infinitely many when and
B.Unique if ; infinitely many for or ; none otherwise
C.Unique if ; infinitely many for or ; none otherwise
D.Unique for every except ; infinitely many when and
Correct Answer: Unique if ; infinitely many for or ; none otherwise
Explanation:
The coefficient determinant is . At , consistency requires ; at , it requires . Each consistent singular case has one free variable.
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46Let and . What is the inverse of ?
inverse of matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , the Sherman–Morrison formula gives , yielding the stated matrix.
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47For which statement is correct?
eigenvalues and eigenvectors
Hard
A.The eigenvalue has algebraic multiplicity and a two-dimensional eigenspace
B.The eigenvalue has algebraic multiplicity and eigenspace
C.The matrix has eigenvalues , , and with distinct eigenvectors
D.The eigenvalue has algebraic multiplicity and eigenspace
Correct Answer: The eigenvalue has algebraic multiplicity and eigenspace
Explanation:
The triangular matrix has only the eigenvalue , repeated three times. Solving forces , so the eigenspace is one-dimensional.
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48Let be a real matrix of rank , and let be a matrix. If is consistent, what is the dimension of its affine solution set in the space of matrices?
solution of linear system of equations
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The nullity of is . Each of the five columns of therefore has one independent homogeneous parameter, giving total affine dimension .
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49Elementary matrices represent row operations applied to an invertible matrix in that order. If the operations reduce to , which expression equals ?
elementary operations of matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Applying the operations in order gives . Therefore, the product multiplying on the left is precisely .
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50In , let , , , and . For which values of are the four vectors linearly independent?
linear dependence and independence of vectors
Hard
A.Exactly when
B.Exactly when
C.Exactly when
D.Exactly when
Correct Answer: Exactly when
Explanation:
The determinant of the matrix with these vectors as columns is proportional to . At , the nontrivial relation holds.
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51Let and . If what is the dimension of the set of vectors satisfying both and ?
rank of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The simultaneous equations form a homogeneous system whose coefficient matrix is the stacked matrix. Rank–nullity gives dimension .
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52Let be invertible and let be nonzero vectors satisfying . Which vector is guaranteed to be a nonzero null vector of ?
inverse of matrices
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Direct substitution gives . Since is invertible and , this null vector is nonzero.
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53For what is the inertia of when ? The inertia lists the numbers of positive, negative, and zero eigenvalues.
eigenvalues and eigenvectors
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The eigenvalues are once and twice. In the given interval, while , so the inertia is .
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54An invertible matrix has eigenvalues , , and , counted with algebraic multiplicity. What is ?
properties of eigenvalues
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The eigenvalues of are . Their sum is .
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55Let satisfy , and suppose has distinct eigenvalues. Which statement must hold?
properties of eigenvalues
Hard
A.Every eigenvector of is also an eigenvector of
B.The eigenvalues of and have equal multiplicities
C.Every eigenvector of is also an eigenvector of
D.The characteristic polynomials of and are equal
Correct Answer: Every eigenvector of is also an eigenvector of
Explanation:
Commutation makes each eigenspace of invariant under . Since every eigenspace of is one-dimensional, acts by scalar multiplication on it.
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56A matrix has characteristic polynomial . Which expression equals ?
Cayley-Hamilton theorem
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Cayley–Hamilton gives . Reducing modulo gives , yielding the result.
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57An invertible matrix has characteristic polynomial . Which formula for follows from the Cayley–Hamilton theorem?
Cayley-Hamilton theorem
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Cayley–Hamilton gives . Multiplying by and rearranging yields .
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58Let be a matrix of rank and a matrix of rank . What is the smallest value that can attain?
rank of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Sylvester's rank inequality gives . This bound is attainable by maximizing the intersection of with the column space of .
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59Let have rank , and suppose with . Which statement correctly classifies ?
solution of linear system of equations
Hard
A.It has no solution if , and a unique solution otherwise
B.It has infinitely many solutions for every vector regardless of
C.It has a unique solution if , and infinitely many solutions otherwise
D.It has infinitely many solutions with one free parameter if , and no solution otherwise
Correct Answer: It has infinitely many solutions with one free parameter if , and no solution otherwise
Explanation:
Consistency requires to be orthogonal to the left nullspace, so . When consistent, , producing one free parameter.
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60A matrix has characteristic polynomial . If and , which conclusion is correct?
eigenvalues and eigenvectors
Hard
A. is not diagonalizable because the eigenspace for has dimension
B. is diagonalizable because both eigenvalues have algebraic multiplicity
C. is not diagonalizable because the eigenspace for has dimension
D. is diagonalizable because the two stated ranks are different
Correct Answer: is not diagonalizable because the eigenspace for has dimension
Explanation:
Nullity gives eigenspace dimensions for and for . The latter is smaller than its algebraic multiplicity , so is not diagonalizable.
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