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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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272 Chapter 8 Matrix algebra

TheeffectofpremultiplyingAbyIhasbeentoleaveAunaltered.Theproductisidentical

tothe originalmatrixA, and this iswhyI iscalled an identitymatrix.

In general, if A is an arbitrary matrix and I is an identity matrix of the appropriate

size,then

IA=A

IfAisasquare matrix thenIA =AI =A.

8.5.4 Thetransposeofamatrix

IfAisanarbitrarym×nmatrix,arelatedmatrixisthetransposeofA,writtenA T ,found

by interchanging the rows and columns ofA. Thus the first row ofAbecomes the first

column ofA T and so on.A T isann ×mmatrix.

( ) 1 −1

Example8.15 IfA = findA

2 4

T .

( )

Solution 1 2

A T =

−1 4

( ) 426

Example8.16 IfA = findA

187

T and evaluateAA T .

⎛ ⎞

4 1

( ) ⎛ ⎞

1

Solution A T = ⎝2 8⎠ 426

AA T = ⎝4

2 8⎠ =

187

6 7

6 7

( ) 56 62

62 114

8.5.5 Symmetricmatrices

IfasquarematrixAanditstransposeA T areidentical,thenAissaidtobeasymmetric

matrix.

⎛ ⎞

5−4 2

Example8.17 IfA = ⎝−4 6 9⎠findA T .

2 913

⎛ ⎞

5−4 2

Solution A T = ⎝−4 6 9⎠

2 913

whichisclearlyequaltoA.HenceAisasymmetricmatrix.Notethatasymmetricmatrix

issymmetrical about its leading diagonal.

8.5.6 Skewsymmetricmatrices

If a square matrixAissuchthatA T = −A thenAissaidtobe skewsymmetric.

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