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Exercise FS.M51 Robert Beezer Suppose that A is a singular matrix. Extend the four conclusions of Theorem FS in this special case and discuss connections with previous results (such as Theorem NME4)

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Final answer:

With a singular matrix A, we cannot conclude that A = B from the matrix equations A × F = B × F, A FB F, or FÃ = BF, because the multiplication by a singular matrix can lead to equal products even for different matrices A and B.

Step-by-step explanation:

The Impact of a Singular Matrix on Matrix Equations

When considering the question of whether matrix equations such as A × F = B × F lead us to conclude that A = B, it is critical to understand the properties of the matrices involved. In the case where A is a singular matrix, we encounter special circumstances that affect our reasoning. Here are the points that need to be discussed:

(a) If A × F = B × F, we cannot necessarily conclude that A = B, because if F is a zero matrix or another singular matrix that nullifies the columns, the products may be the same even for different A and B.

(b) Similarly, if A FB F, the same logic applies, and without additional information, A = B cannot be conclusively stated.

(c) In the equation FÃ = BF, we are faced with the transposed form of A (denoted Ã) being multiplied by F. Again, because multiplying by a singular matrix can yield a zero product, we cannot conclusively deduce that A = B from this equation alone.

The implications of a singular matrix in such matrix equations speak to broader algebraic principles, including the non-invertibility of singular matrices and their role in determining the solution sets of linear systems. Theorem FS and Theorem NME4 both relate to the behavior of non-singular (invertible) matrices and the unique solutions of linear systems, underscoring the fact that when dealing with singular matrices, such uniqueness may not hold.

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