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Which three matrices E_{21}, E_{31}, E_{32}, put A into triangular form U?

A =

[1 1 0]

[4 6 1]

[-2 2 0]

and E_{32}E_{31}E_{21}A = U.

Multiply those E's to get one matrix M that does elimination: MA = U.

Attempt at a solution

I already found all the E's. What I don't get is, if it didn't tell me E_{32}E_{31}E_{21}A = U, how would I know the correct order of multiplication in for M? In other words, how do I know M = E_{32}E_{31}E_{21}instead of E_{21}E_{31}E_{32}

edit- Thanks Tedjn, HallsofIvy

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# Homework Help: Quick basic lin alg quest

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