Why Does Sum of Matrix Elements x Cofactor in Different Rows Equal Zero?

In summary, the determinant value of a matrix can be calculated by multiplying the sum of elements in a row with its corresponding cofactor. However, when replacing one row with another in a square matrix, the determinant value remains the same because the elements and cofactors remain the same, resulting in a determinant value of det B for the new matrix.
  • #1
ajayguhan
153
1
In a matrix the sum of element of a matrix in a row times it's co factor of that elemt gives the determinant value, but why does the sum of element of a matrix times cofactor of different row is always zero?
 
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In a square matrix A, replace row j by row i, obtaining a new matrix B with row i and row j being equal. Expanding using elements from row i in A and cofactors corresponding to row j in A will be the same as expanding det B along row j (using cofactors corresponding to row j in B also) since the elements and cofactors are the same in both cases. So the result is det B, which is...?
 
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What is a matrix?

A matrix is a mathematical structure that consists of rows and columns of numbers. It is commonly used in linear algebra and has many applications in fields such as physics, engineering, and computer graphics.

What is a cofactor?

A cofactor is a number that is calculated from the elements of a matrix. It is used in various matrix operations, such as finding the inverse of a matrix or solving systems of linear equations.

Why does the sum of matrix elements multiplied by their cofactors equal zero?

This is because of the properties of determinants, which are closely related to cofactors. When we expand a determinant along a particular row or column, we can see that the elements are multiplied by their cofactors. Since the determinant of a matrix with all zeros in a particular row or column is zero, the sum of the elements multiplied by their cofactors must also be zero.

What is the significance of this property?

This property is important because it allows us to solve systems of linear equations using the inverse of a matrix. By finding the cofactors of a matrix and using them to form the adjugate matrix, we can find the inverse of the original matrix. This, in turn, allows us to solve systems of linear equations, which have many real-world applications.

Can this property be extended to matrices of any size?

Yes, this property holds true for matrices of any size. The sum of matrix elements multiplied by their cofactors will always equal zero, as long as the matrix is square (has the same number of rows and columns).

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