Precalculus : Matrices and Vectors

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Find The Multiplicative Inverse Of A Matrix

What is the inverse of the following nxn matrix 

 

Possible Answers:

The matrix is not invertible.

Correct answer:

The matrix is not invertible.

Explanation:

Note the first and the last columns are equal.

Therefore, when we try to find the determinant using the following formula we get the determinant equaling 0:

This means simply, that the matrix does not have an inverse.

 

Example Question #1 : Find The Multiplicative Inverse Of A Matrix

Find the inverse of the matrix

.

Possible Answers:

Does not exist

Correct answer:

Does not exist

Explanation:

For a 2x2 matrix

the inverse can be found by 

Because the determinant is equal to zero in this problem, or

,

the inverse does not exist.

Example Question #2 : Find The Multiplicative Inverse Of A Matrix

Find the inverse of the matrix.

Possible Answers:

Correct answer:

Explanation:

We use the inverse of a 2x2 matrix formula to determine the answer. Given a matrix 

 it's inverse is given by the formula:

First we define the determinant of our matrix:

Then, 

 

Example Question #1 : Find The Multiplicative Inverse Of A Matrix

Find the inverse of the following matrix.

Possible Answers:

This matrix has no inverse.

Correct answer:

This matrix has no inverse.

Explanation:

This matrix has no inverse because the columns are not linearly independent. This means if you row reduce to try to compute the inverse, one of the rows will have only zeros, which means there is no inverse.

Example Question #1 : Find The Multiplicative Inverse Of A Matrix

Find the multiplicative inverse of the following matrix:

 

Possible Answers:

This matrix has no inverse.

Correct answer:

Explanation:

By writing the augmented matrix , and reducing the left side to the identity matrix, we can implement the same operations onto the right side, and we arrive at , with the right side representing the inverse of the original matrix.

Example Question #71 : Matrices And Vectors

Find the inverse of the matrix 

Possible Answers:

None of the other answers.

Correct answer:

Explanation:

There are a couple of ways to do this. I will use the determinant method.

First we need to find the determinant of this matrix, which is

 

for a matrix in the form:

 .

Substituting in our values we find the determinant to be:

Now one formula for finding the inverse of the matrix is

 

.

Example Question #1 : Solve A System Of Equations Using The Multiplicative Inverse

What is the inverse of the identiy matrix   ?

Possible Answers:

The identity matrix 

Correct answer:

The identity matrix 

Explanation:

By definition, an inverse matrix is the matrix B that you would need to multiply matrix A by to get the identity. Since the identity matrix yields whatever matrix it is being multiplied by, the answer is the identity itself.

Example Question #1 : Solve A System Of Equations In Three Variables Using Augmented Matrices

Express this system of equations as an augmented matrix:

 

Possible Answers:

Correct answer:

Explanation:

Arrange the equations into the form:

, where a,b,c,d are constants.

Then we have the system of equations: .

The augmented matrix is found by copying the constants into the respective rows and columns of a matrix.

The vertical line in the matrix is analogous to the = sign thus resulting in the following:

Example Question #2 : Solve A System Of Equations In Three Variables Using Augmented Matrices

Using an augmented matrix, solve the following system of equations:

 

Which of the following are the values of ,,and  that satisfy this system?

 

Possible Answers:

Correct answer:

Explanation:

Create an augmented matrix by entering the coefficients into one matrix and appending a vector to that matrix with the constants that the equations are equal to. Then you can row reduce to solve the system.

First, lets make this augmented matrix:

 

Now we can row reduce the matrix using the three row reduction operations: mutliply a row, add one row to another, swap row positions.

 

First, we can subtract 

Swap 

Subtract 

Add  

Subtract 

Mulitply 

 

You can stop here given that this augmented matrix can be rewritten as a system again with

 , or you can continue using the matrix, subtracting multiples of  from the other two rows to get an identity matrix yielding the solution to the system. 

 

 

 

Example Question #14 : Finite Mathematics

True or false: there is no  solution  that makes this matrix equation true.

Possible Answers:

True

False

Correct answer:

False

Explanation:

For two matrices to be equal, two conditions must hold:

1) The matrices must have the same dimension. This can be seen to be the case, since both matrices have two rows and one column.

2) All corresponding entries must be equal. For this to happen, it must hold that

This is a system of two equations in two variables, which can be solved as follows:

Add both sides of the equations:

It follows that

Substitute back:

Thus, there exists a solution to the system, and, consequently, to the original matrix equation. The statement is therefore false.

 

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