Elementary operations and their use in getting the rank of a matrix
Easy
A.Adding two columns only
B.Interchanging two rows
C.Deleting a row
D.Squaring a row
Correct Answer: Interchanging two rows
Explanation:
Interchanging two rows is one of the three elementary row operations.
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2The rank of a matrix is the maximum number of linearly independent:
Elementary operations and their use in getting the rank of a matrix
Easy
A.Diagonal entries
B.Rows or columns
C.Zero entries
D.Eigenvalues only
Correct Answer: Rows or columns
Explanation:
The rank is the maximum number of linearly independent rows or columns of a matrix.
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3What is the rank of the zero matrix of order ?
Elementary operations and their use in getting the rank of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
A zero matrix has no nonzero linearly independent rows or columns, so its rank is .
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4Which elementary operation does not change the rank of a matrix?
Elementary operations and their use in getting the rank of a matrix
Easy
A.Multiplying a row by a nonzero number
B.Replacing a row by zero
C.Deleting an independent row
D.Changing every entry to its square
Correct Answer: Multiplying a row by a nonzero number
Explanation:
Elementary row operations, including multiplication by a nonzero number, preserve the rank of a matrix.
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5A square matrix has an inverse if and only if:
Inverse of a matrix
Easy
A.
B. has a zero row
C.
D. is rectangular
Correct Answer:
Explanation:
A square matrix is invertible precisely when its determinant is nonzero.
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6If is the inverse of , then equals:
Inverse of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
By definition of an inverse, , where is the identity matrix.
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7What is the inverse of the identity matrix ?
Inverse of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The identity matrix multiplied by itself gives , so .
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8For , the determinant of is:
Inverse of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
For a matrix, the determinant is calculated as .
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9If is a square matrix and exists, then is called:
Inverse of a matrix
Easy
A.Nonsingular
B.Rectangular
C.Zero
D.Singular
Correct Answer: Nonsingular
Explanation:
A square matrix with an inverse is called nonsingular or invertible.
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10The equations and have the solution:
Solution of linear simultaneous equations
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Adding the equations gives , so . Substitution gives .
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11A system of linear equations is consistent if it has:
Solution of linear simultaneous equations
Easy
A.More variables than equations
B.Only zero coefficients
C.At least one solution
D.No solution
Correct Answer: At least one solution
Explanation:
A consistent system has at least one solution, either unique or infinitely many.
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12The matrix form of a system of linear equations is commonly written as:
Solution of linear simultaneous equations
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
A system of linear equations can be represented compactly as .
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13If the coefficient matrix is invertible in , the solution is:
Solution of linear simultaneous equations
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
Multiplying on the left by gives .
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14The equations and represent:
Solution of linear simultaneous equations
Easy
A.A single point
B.Two parallel lines
C.The same line
D.Two perpendicular lines
Correct Answer: The same line
Explanation:
The second equation is twice the first, so both equations represent the same line and have infinitely many solutions.
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15A scalar is an eigenvalue of if there is a nonzero vector such that:
Eigen-values and eigenvectors of a matrix
Easy
A.
B. for every
C.
D.
Correct Answer:
Explanation:
An eigenvalue satisfies for some nonzero vector .
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16An eigenvector of a matrix must be:
Eigen-values and eigenvectors of a matrix
Easy
A.A determinant
B.A nonzero vector
C.A zero vector
D.A scalar only
Correct Answer: A nonzero vector
Explanation:
An eigenvector is required to be nonzero; the zero vector cannot define an eigenvalue.
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17The eigenvalues of a matrix are found from the equation:
Eigen-values and eigenvectors of a matrix
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
The equation is called the characteristic equation.
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18The eigenvalues of a diagonal matrix are its:
Eigen-values and eigenvectors of a matrix
Easy
A.Column products
B.Row sums
C.Off-diagonal entries
D.Diagonal entries
Correct Answer: Diagonal entries
Explanation:
For a diagonal matrix, the diagonal entries are its eigenvalues.
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19If and is an eigenvector, then cannot be:
Eigen-values and eigenvectors of a matrix
Easy
A.An eigenvector
B.A nonzero vector
C.The zero vector
D.A column vector
Correct Answer: The zero vector
Explanation:
The zero vector is excluded from the definition of an eigenvector.
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20The Cayley-Hamilton theorem states that every square matrix satisfies its own:
Cayley-Hamilton theorem
Easy
A.Characteristic equation
B.Linear equation
C.Row equation
D.Inverse equation
Correct Answer: Characteristic equation
Explanation:
The theorem states that a square matrix satisfies the polynomial equation obtained from its characteristic polynomial.
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21Find the rank of the matrix .
Elementary operations and their use in getting the 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, so .
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22For , what is the rank when ?
Elementary operations and their use in getting the rank of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The second row is twice the first. When , the third row is not a multiple of the first, giving two independent rows. Hence, the rank is .
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23Which elementary row operation leaves the rank of a matrix unchanged?
Elementary operations and their use in getting the rank of a matrix
Medium
A.Replacing a row by its square
B.Deleting a nonzero row
C.Multiplying a row by zero
D.Adding a multiple of one row to another
Correct Answer: Adding a multiple of one row to another
Explanation:
Replacing one row by itself plus a multiple of another row is an invertible elementary operation and preserves the rank.
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24The echelon form of a matrix is . What is its rank?
Elementary operations and their use in getting the rank of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The rank equals the number of nonzero rows, or equivalently the number of pivots. There are two nonzero rows.
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25Find the inverse of .
Inverse of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , .
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26For which value of does the matrix fail to have an inverse?
Inverse of a matrix
Medium
A.
B.
C.
D. only
Correct Answer:
Explanation:
The determinant is . The matrix is singular when , so . Among the listed choices, is correct.
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27If is a nonsingular matrix and , then which statement is necessarily true?
Inverse of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
For a nonsingular square matrix, the matrix that satisfies is the inverse of . Thus, .
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28Find the inverse of .
Inverse of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Solving by forward substitution gives .
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29Solve the system and .
Solution of linear simultaneous equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Adding the equations gives , so . Substitution into gives .
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30Determine the nature of the solutions of , , and .
Solution of linear simultaneous equations
Medium
A.A unique solution
B.Exactly two solutions
C.No solution
D.Infinitely many solutions
Correct Answer: No solution
Explanation:
The first and third equations have identical left-hand sides but different constants, which is inconsistent. Therefore, the system has no solution.
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31For the system and , when does the system have infinitely many solutions?
Solution of linear simultaneous equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
For infinitely many solutions, the second equation must be twice the first. Thus, , giving .
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32Using Cramer's rule, find in the system and .
Solution of linear simultaneous equations
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The determinant is . Replacing the first column gives determinant . Hence, .
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33Find the eigenvalues of .
Eigen-values and eigenvectors of a matrix
Medium
A. and
B. and
C. and
D. and
Correct Answer: and
Explanation:
The characteristic equation is , which factors as .
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34An eigenvector corresponding to the eigenvalue of is:
Eigen-values and eigenvectors of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
For , gives . Therefore, any nonzero multiple of is an eigenvector.
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35If the eigenvalues of a matrix are , , and , what is its trace?
Eigen-values and eigenvectors of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The trace of a matrix equals the sum of its eigenvalues. Thus, .
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36If is an eigenvalue of an invertible matrix , which is an eigenvalue of ?
Eigen-values and eigenvectors of a matrix
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
From with , multiplying by gives .
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37For , what is the algebraic multiplicity of its eigenvalue?
Eigen-values and eigenvectors of a matrix
Medium
A.The eigenvalue has multiplicity
B.The eigenvalue has multiplicity
C.The eigenvalue has multiplicity
D.The eigenvalue has multiplicity
Correct Answer: The eigenvalue has multiplicity
Explanation:
Since is upper triangular, its eigenvalues are its diagonal entries. Both diagonal entries are , so has algebraic multiplicity .
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38The characteristic polynomial of is . By the Cayley-Hamilton theorem, which equation is satisfied by ?
Cayley-Hamilton theorem
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The Cayley-Hamilton theorem states that a matrix satisfies its own characteristic equation. Replacing by gives .
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39If a matrix satisfies , express in terms of and .
Cayley-Hamilton theorem
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
Rearranging gives . Multiplying by shows that .
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40If , find in terms of and .
Cayley-Hamilton theorem
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
From , multiply by to obtain .
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41For the matrix , determine its rank according to the value of .
Elementary operations and their use in getting the rank of a matrix
Hard
A. for all
B. for all
C. if , and otherwise
D. if , and otherwise
Correct Answer: if , and otherwise
Explanation:
The second row is twice the first. Replacing the third row by gives . Thus the rank is when and otherwise.
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42Let be a matrix whose reduced row-echelon form is . Which statement is necessarily true?
Elementary operations and their use in getting the rank of a matrix
Hard
A.The fourth column is a pivot column of the original matrix
B.The nullity of is
C.Every solution of has its third component equal to zero
D.The column space of has dimension
Correct Answer: The column space of has dimension
Explanation:
There are three pivots, so . Hence the column-space dimension is , while the nullity is .
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43For , find the values of for which .
Elementary operations and their use in getting the rank of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Subtracting twice the first row from the second and the first row from the third gives rows and . The determinant is therefore zero precisely when .
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44Which operation can change the numerical values of minors but cannot change the rank of a matrix?
Elementary operations and their use in getting the rank of a matrix
Hard
A.Deleting a nonzero row
B.Multiplying a row by a nonzero scalar
C.Multiplying a row by the zero scalar
D.Replacing a row by a non-equivalent linear combination
Correct Answer: Multiplying a row by a nonzero scalar
Explanation:
Scaling a row by a nonzero scalar preserves linear dependence and therefore preserves rank. The zero scalar and arbitrary deletion or replacement can alter rank.
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45The inverse of is
Inverse of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The determinant of is . Computing the cofactor adjugate gives , so .
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46For , which matrix satisfies ?
Inverse of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , the inverse is .
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47Suppose a square matrix satisfies . Which expression gives ?
Inverse of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The relation gives . Therefore .
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48Let be an matrix. If , which conclusion is always valid?
Inverse of a matrix
Hard
A.
B. is necessarily singular
C. has no eigenvalue equal to
D.
Correct Answer:
Explanation:
Rearranging gives , so is invertible and .
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49Consider the system , , and . Which condition gives infinitely many solutions?
Solution of linear simultaneous equations
Hard
A. and
B. and
C. and
D. and
Correct Answer: and , or and
Explanation:
The first two equations are dependent. If , consistency requires and leaves one free variable. If , consistency also requires and leaves two free variables.
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50For the system , , and , the solution set is
Solution of linear simultaneous equations
Hard
A.A two-parameter family of solutions
B.No solution
C.A one-parameter family of solutions
D.A unique solution
Correct Answer: A one-parameter family of solutions
Explanation:
The third equation is the sum of the first two, so it is redundant. The first two independent equations in three unknowns leave one free parameter.
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51For the system , , and , determine the value of for consistency.
Solution of linear simultaneous equations
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The left side of the third equation equals the second left side minus the first left side. Therefore its right side must be .
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52If the coefficient matrix of a system has rank and the augmented matrix has rank , then the system has
Solution of linear simultaneous equations
Hard
A.Exactly two solutions
B.Infinitely many solutions
C.No solution
D.A unique solution
Correct Answer: No solution
Explanation:
Consistency requires . Since the ranks differ, the system is inconsistent.
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53For , which pair correctly gives an eigenvalue and a corresponding eigenvector?
Eigen-values and eigenvectors of a matrix
Hard
A.,
B.,
C.,
D.,
Correct Answer: ,
Explanation:
The matrix is upper triangular, so its eigenvalues are . Solving gives .
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54For , the eigenspace corresponding to is
Eigen-values and eigenvectors of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Since , vectors orthogonal to have eigenvalue . This two-dimensional space is described by .
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55The matrix is not diagonalizable because
Eigen-values and eigenvectors of a matrix
Hard
A.It has no real eigenvalues
B.Its characteristic polynomial has no repeated root
C.Its eigenspace has dimension less than the algebraic multiplicity
D.Its determinant is equal to zero
Correct Answer: Its eigenspace has dimension less than the algebraic multiplicity
Explanation:
The only eigenvalue is with algebraic multiplicity , but solving gives a one-dimensional eigenspace. Thus is defective.
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56If a matrix has characteristic polynomial and the eigenspace for has dimension , which statement is correct?
Eigen-values and eigenvectors of a matrix
Hard
A.The matrix is diagonalizable
B.The eigenvalue has geometric multiplicity zero
C.The matrix is not diagonalizable
D.The matrix has three linearly independent eigenvectors
Correct Answer: The matrix is not diagonalizable
Explanation:
The eigenvalue requires two independent eigenvectors for diagonalizability, but its eigenspace has dimension . Hence the matrix is not diagonalizable.
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57If is an eigenvector of an invertible matrix with eigenvalue , which is necessarily true?
Eigen-values and eigenvectors of a matrix
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
From and invertibility, applying gives , hence .
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58A matrix has characteristic polynomial . Using the Cayley-Hamilton theorem, express in terms of , , and .
Because the constant term is nonzero, is invertible. Multiplying the relation by gives .
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60Let be a matrix with characteristic polynomial . Which identity follows directly from Cayley-Hamilton?
Cayley-Hamilton theorem
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Substitute into : . Rearrangement gives the stated identity.
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