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Find `A^(-1)` if `A=|(0,1,1),(1,0,1),(1,1,0)|` and show that `A^(-1)=(A^(2)-3I)/2` |
Answer» We have, `A[(0,1,1),(1,0,1),(1,1,0)]` Cofactors are `A_(11)=-1, A_(12)=1, A_(13)=1`, `A_(21)=1, A_(22)=-1, A_(23)=1`, `A_(31)=1, A_(31)=1, A_(32)=1 A_(33)=-1` `:." adj A"=[(-1,1,1),(1,-1,1),(1,1,-1)]^(T)=[(-1,1,1),(1,-1,1),(1,1,-1)]` `|A|=0-(-1)+1.1=2` `:. A^(-1)=("adj A")/(|A|)=1/2 [(-1,1,1),(1,-1,1),(1,1,-1)]` Now `A^(2)=[(0,1,1),(1,0,1),(1,1,0)][(0,1,1),(1,0,1),(1,1,0)]=[(2,1,1),(1,2,1),(1,1,2)]` `:. (A^(2)-3I)/2=1/2 {[(2,1,1),(1,2,1),(1,1,2)]-[(3,0,0),(0,3,0),(0,0,3)]}` `=1/2 |(-1,1,1),(1,-1,1),(1,1,-1)|=A^(-1)` Hence proved. |
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