All Linear Algebra Resources
Example Questions
Example Question #352 : Operations And Properties
True or false: Square matrix is nilpotent if and only if .
False
True
False
A square matrix is nilpotent if, for some whole number , , the zero matrix of the same dimension as .
The determinant of the product of matrices is equal to the product of their determinants. It follows that if , , so . Therefore, any nilpotent matrix must have determinant 0.
However, not all matrices with determinant 0 are nilpotent, as is proved by counterexample. Let
This matrix is diagonal, as its only nonzero entry is alone its main diagonal. To raise this to a power , simply raise all of the diagonal elements to the power of , and preserve the off-diagonal zeroes. It follows that for all ,
Also, the determinant of is .
Since a non-nilpotent matrix with determinant zero exists, the biconditonal is false.
Example Question #41 : The Determinant
, , and are each real matrices.
; ; .
True or false: It follows that is a singular matrix.
False
True
True
The determinant of the product of matrices is equal to the product of their determinants; thus,
.
A matrix has determinant 0 if and only if it is singular - that is, without an inverse. It therefore follows that is singular.
Example Question #43 : The Determinant
Let , , and be three noncollinear points in Cartesian three-space. The equation of the plane through all three points is
Give the equation of the plane that includes the points , , and .
If the three known points , , and , and an unknown point are coplanar, then
The variable equation can be formed from this determinant equation.
Using the first row, this can be rewritten as
,
where , the minor, is the determinant of the matrix formed by striking out Row 1 and Column 4:
Adding the upper-left to lower-right products and subtracting the upper-right to lower left products:
Set this equal to 0 to get the equation of the plane:
Example Question #42 : The Determinant
, , and are each real matrices.
; ; .
True or false: It follows that is a nonsingular matrix.
True
False
False
The statement can be proved false through counterexample.
Let
Each of the matrices has only zero elements on its off-diagonal elements, so each is a diagonal matrix. Consequently, the determinant of each matrix is the product of its diagonal elements.
is a zero matrix, so ; is an identity matrix, so ; and
, , and meet the conditions of the problem. Now, add the matrices by adding corresponding entries:
This matrix is also diagonal, so
A matrix has determinant 0 if and only if it is singular - that is, without an inverse. It therefore follows that is singular. Thus, we have proved through counterexample that need not be nonsingular.
Example Question #41 : The Determinant
, , and are each real matrices.
; ; .
True or false: It follows that is a singular matrix.
True
False
False
The statement can be proved false through counterexample.
Let
Each of the matrices has only zero elements on its off-diagonal elements, so each is a diagonal matrix. Consequently, the determinant of each matrix is the product of its diagonal elements.
is a zero matrix, so ; is an identity matrix, so ; and
, , and meet the conditions of the problem. Now, add the matrices by adding corresponding entries:
This matrix is also diagonal, so
A matrix has a nonzero determinant if and only if it is nonsingular - that is, with an inverse. It therefore follows that is nonsingular. Thus, we have proved through counterexample that need not be singular.
Example Question #44 : The Determinant
Let , , , and be three points in Cartesian three-space. These points are coplanar if and only if
Three points are given: , , and . Which point along the line of the equation
is on the plane that includes these points?
None of the other choices gives the correct response.
The three points , , and , and a point of the form
for some real are on the same plane. Therefore, it follows that we must find so that
Using the first row, this can be rewritten as
,
where , the minor, is the determinant of the matrix formed by striking out Row 1 and Column 4:
Adding the upper-left to lower-right products and subtracting the upper-right to lower left products:
Thus,
,
and
et this equal to 0 and solve for :
The desired point is .
Example Question #47 : The Determinant
Let , , , and be three points in Cartesian three-space. These points are coplanar if and only if
Three points are given: , , and . Which point along the line of the equation
is on the plane that includes these points?
None of the other choices gives the correct response.
The three points , , and , and a point of the form for some real are on the same plane. Therefore, it follows that we must find so that
Using the first row, this can be rewritten as
,
where , the minor, is the determinant of the matrix formed by striking out Row 1 and Column 4:
Adding the upper-left to lower-right products and subtracting the upper-right to lower left products:
It follows that
,
and
Set this equal to 0 to find :
The desired point is .
Example Question #354 : Operations And Properties
, , and are each real matrices.
; ; .
True or false: It follows that is a nonsingular matrix.
False
True
False
The statement can be proved false through counterexample.
Let
Each of the matrices has only zero elements on its off-diagonal elements, so each is a diagonal matrix. Consequently, the determinant of each matrix is the product of its diagonal elements.
is a zero matrix, so ; is an identity matrix, so ; and
, , and meet the conditions of the problem. Now, add the matrices by adding corresponding entries:
This matrix is also diagonal, so
A matrix has determinant 0 if and only if it is singular - that is, without an inverse. It therefore follows that is singular. Thus, we have proved through counterexample that need not be nonsingular.
Example Question #43 : The Determinant
for some real such that has an inverse.
Give in terms of .
None of the other choices gives the correct response.
The inverse of a two-by-two matrix
is the matrix
.
is the determinant of the matrix, which is the product of the main diagonal elements minus the product of the other two:
The inverse is
.
Example Question #44 : The Determinant
Find .
The inverse of a two-by-two matrix
is the matrix
.
is the determinant of the matrix, which is the product of the main diagonal elements minus the product of the other two:
Therefore,