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A=[tex] \left[\begin{array}{ccc}1&-1\\2&2&\\\end{array}\right] [/tex]

B=[tex] \left[\begin{array}{ccc}1&1\\a&b&\\\end{array}\right] [/tex]


Aratati ca det(A+x×[tex]I_{2}[/tex])>0 aricare ar fi x apartine lui R