What Is the Value of k That Makes This Matrix Non-Invertible?

In summary, the conversation focuses on determining the value of k for which the matrix (2 4 1) (k -1 2) (7 7 4) has no inverse. The answer is believed to be k = 1, but there is confusion as one person obtained a different answer of -3. The conversation also mentions using a calculator and Matlab to double check the result, and advises checking signs carefully when reworking the problem.
  • #1
wayneo
31
0
determine the value of k for which the matrix

(2 4 1)
(k -1 2)
(7 7 4) has no inverse

apparently the answer is k = 1 but I can't see how.

I worked it out to be -3
 
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  • #2
Can you show your work?

I obtained an answer that isn't k=1, by the way. Are you sure you copied the matrix and/or the answer down correctly ?
 
Last edited:
  • #3
I agree that it is not one, but I don't agree with your answer of -3. Assuming that the matrix you gave is correct, look back at your working (preferably post what you have done) - I checked my result with my calculator, and found the matrix to be singular.
 
  • #4
see I just wanted to be sure whether the book was wrong or not as it says it is 1. I tried working out the determinant step by step and making it equal to 0 then solve for 'k' like an algebra equation
 
  • #5
I worked it out to be neither 1 nor -3, and double checked in matlab.

rework and check your signs carefully.
 

1. What is a matrix and how is it used in math?

A matrix is a rectangular array of numbers or symbols arranged in rows and columns. It is used in math to represent and solve systems of linear equations, perform operations on vectors, and transform geometric shapes.

2. How do you add or subtract matrices?

To add or subtract matrices, the matrices must have the same dimensions (same number of rows and columns). Simply add or subtract the corresponding elements in each matrix to get the resulting matrix.

3. What is matrix multiplication and how is it performed?

Matrix multiplication is a way to combine two matrices to get a new matrix. It is performed by multiplying the rows of the first matrix by the columns of the second matrix and adding the products. The resulting matrix will have the same number of rows as the first matrix and the same number of columns as the second matrix.

4. How do you find the inverse of a matrix?

The inverse of a matrix is a matrix that when multiplied by the original matrix results in the identity matrix. To find the inverse, the original matrix must be square and have a non-zero determinant. The inverse can be found using various methods, such as Gaussian elimination or the adjugate matrix method.

5. What are the practical applications of matrices?

Matrices have many practical applications in fields such as engineering, physics, computer graphics, and economics. They are used to solve systems of equations, calculate transformations, analyze data, and more. Some specific examples include using matrices to model traffic flow, analyze stock market trends, and design computer generated images.

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