Is the Matrix A with Entries aij=min(i,j) Always Invertible?

RobandJoanna
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Help! System of equations!

For a natural number define the n*n matrix A = (aij) by setting aij = min(i,j). Write down the matrix a for a few values of n = 2,3,4... Show that A is invertible and find its inverse.
Hence or otherwise show that the system of equations Ax =b , where x=(x1,...xn) and b=(b1...bn) has a unique solution.

Anyone help with how to solve that?
Thanks
Rob and Joanna!
 
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Have you tried n=2, 3, and 4 at least?

Write them down and try to reduce to the identity by row operations. Should be easy. You shold be able to find inverse in each case too.
 


Hi Rob and Joanna,

Solving systems of equations can be challenging, but with some practice and understanding of certain concepts, it can become easier. Let's first start by defining what a system of equations is. A system of equations is a set of two or more equations with multiple variables that need to be solved simultaneously.

In this case, we have a system of equations represented by the matrix A and vector x. The first step in solving this system is to understand the properties of the given matrix A. From the given definition, we can see that A is a lower triangular matrix, which means that all the entries above the main diagonal are zero.

For n = 2, the matrix A would look like this:

A = [1 0
0 2]

Similarly, for n = 3, the matrix A would be:

A = [1 0 0
0 2 0
0 0 3]

We can see that for any value of n, the matrix A will always be invertible. This is because the determinant of a lower triangular matrix is equal to the product of its diagonal entries, which in this case is always greater than zero. Therefore, we can find the inverse of A using the formula:

A^-1 = 1/det(A) * adj(A)

Where adj(A) is the adjugate matrix of A. Using this formula, we can find the inverse of A for any value of n.

Now, coming to the system of equations Ax = b, we can see that the matrix A is invertible, which means that it has a unique solution. This is because the inverse of A exists and is unique. We can find the solution by multiplying both sides of the equation by A^-1, giving us:

x = A^-1 * b

Using the inverse we calculated earlier, we can easily find the solution to this system of equations.

I hope this helps in understanding how to solve systems of equations using matrices. If you have any further doubts, please let me know. Keep practicing and you'll become a pro in no time!


 
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