If (a,b) is a multiple of (c,d) with abcd 6= 0, show that (a,c) is a multiple of (b,d)
Chapter 1, Problem 1.2.22(choose chapter or problem)
If (a,b) is a multiple of (c,d) with abcd 6= 0, show that (a,c) is a multiple of (b,d). This is surprisingly important: call it a challenge question. You could use numbers first to see how a, b, c, and d are related. The question will lead to: If A = a b c d has dependent rows then it has dependent columns.
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