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Question Number 98661 by bemath last updated on 15/Jun/20
using cayley − hamilton  theorem what is the inverse of  matrix A=  [((0    1   −1)),((1    2      2)),((0    1   −1)) ]
usingcayleyhamiltontheoremwhatistheinverseofmatrixA=[011122011]
Commented by john santu last updated on 15/Jun/20
we first compute the characteristic  equation ∣A−λI∣=0   [((−λ       1          −1 )),((   1      2−λ          2)),((    0         1      −1−λ)) ]= 0  = −λ{(2−λ)(−1−λ)−2}−(−1−λ)−1  = λ{λ^2 −λ−4}+1+λ−1  = λ^3 −λ^2 −3λ   the cayley−hamilton theorem  states that a matrix satisfies its  own characteristic equation   ⇒A^3 −A^2 −3A = 0  A(A^2 −A−3I) = 0  ⇔I = (1/3)A(A−I)  ⇔A^(−1)  = (1/3)(A−I)   ⇔A^(−1) = (1/3)  [((−1    1     −1)),((    1      1          2)),((    0     1       −2)) ]
wefirstcomputethecharacteristicequationAλI∣=0[λ1112λ2011λ]=0=λ{(2λ)(1λ)2}(1λ)1=λ{λ2λ4}+1+λ1=λ3λ23λthecayleyhamiltontheoremstatesthatamatrixsatisfiesitsowncharacteristicequationA3A23A=0A(A2A3I)=0I=13A(AI)A1=13(AI)A1=13[111112012]

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