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If `A=[(1,0,0),(0,1,1),(0,-2,4)],6A^-1=A^2+cA+dI,` then `(c,d)=`A. (-6,11)B. (-11,6)C. (11,6)D. (6,11)

Answer» Correct Answer - A
Every square matrix A satisfies its characteristic equation i.e. `abs(A-lambdal)=0`.
Here, `abs(A_lambdal)=0`
`{:rArr abs((1-lambda,0,0),(0,1-lambda,1),(0,-2,4-lambda))=0:}`
`rArr (1-lambda){(1-lambda)(4-lambda)+2}=0`
`rArr lambda^3-6lambda^2+11lambda-6=0`
`rArr A^3 -6A^2+11A-6l=0`
`rArr 6I=A^3-6A^2+11A`
`rArr 6A^(-1)=A^2-6A+11I` [Multiplying both sides by `A^(-1)`]
`:. 6A^(-1) =A^2=cA+dl rArrc=-6and d=11`


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