Engineering
Mathematics
Algebra of Matrices
Multiplication of Matrices
Question

Show that AB ≠ BA in the following matrices:
A=[ 104111 509 50] and B= [1 213 421 32].

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Solution
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L.H.S =AB=[10411150950]3×3[121342132]3×3.
AB=[1012120163108211+15+022+20+011+10+0915+01820+0910+0]3×3
AB=[310421621]3×3           .........(1)
R.H.S =BA=[121342132]3×3[10411150950]3×3
BA=[1022+94+1051+0+03044+1812+20103+0+01033+184+15101+0+0]3×3
=[311423511]3×3            ..........(2)
From (1) and (2) we have L.H.S ≠ R.H.S
Hence AB ≠ BA
Hence proved.