Show that if a square matrix A has two equal columns, then A is not invertible.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Linear Algebra

Show that if a square matrix A has two equal columns, then A is not invertible.
Let A be the square matrix with columns vi v2...vn. Since two of the columns are equal, it must be that v =
Vj
for some i, j. Let H be the rref(A). What can you say about leading ones in the columns i and j? What does
that tell you about the rank of H and hence the rank of A?
Transcribed Image Text:Show that if a square matrix A has two equal columns, then A is not invertible. Let A be the square matrix with columns vi v2...vn. Since two of the columns are equal, it must be that v = Vj for some i, j. Let H be the rref(A). What can you say about leading ones in the columns i and j? What does that tell you about the rank of H and hence the rank of A?
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