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Question

For any 3×3 matrix M, let |M| denote the determinant of M. Let I be the 3×3 identify matrix. Let E and F be two 3×3 matrices such that (IEF) is invertible. If G=(IEF)1, then which of the following statements is(are) TRUE?

A
|FE|=|IFE||FGE|
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B
(IFE)(I+FGE)=I
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C
EFG=GEF
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D
(IFE)(IFGE)=I
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Solution

The correct option is C EFG=GEF
G=(IEF)1
G(IEF)=(IEF)G=I (1)

|IFE||FGE|
=|FGEFEFGE|
=|FGEF(GI)E| (From (1))
=|FGEFGE+FE|
=|FE|
|FE|=|IFE||FGE|


(IFE)(I+FGE)
=I+FGEFEFEFGE
=I+FGEFEF(GI)E (From (1))
=I+FGEFEFGE+FE
=I
(IFE)(I+FGE)=I


From (1), we have
G(IEF)=(IEF)G
GGEF=GEFG
GEF=EFG


(IFE)(IFGE)
=IFGEFE+FEFGE
=IFGEFE+F(GI)E (From (1))
=IFGEFE+FGEFE
=I2FEI

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