Chapter 6: Problem 4
Let \(A\) be a nonsingular matrix and let \(\lambda\) be an eigenvalue of \(A .\) Show that \(1 / \lambda\) is an eigenvalue of \(A^{-1}\)
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Chapter 6: Problem 4
Let \(A\) be a nonsingular matrix and let \(\lambda\) be an eigenvalue of \(A .\) Show that \(1 / \lambda\) is an eigenvalue of \(A^{-1}\)
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Let \(A\) be a diagonalizable matrix whose eigenvalues are all either 1 or \(-1 .\) Show that \(A^{-1}=A\)
Let \(A\) be a symmetric positive definite matrix and let \(Q\) be an orthogonal diagonalizing matrix. Use the factorization \(A=Q D Q^{T}\) to find a nonsingular matrix \(B\) such that \(B^{T} B=A\)
Show that if \(A\) is symmetric positive definite, then \(\operatorname{det}(A)>0 .\) Give an example of a \(2 \times 2\) matrix with positive determinant that is not positive definite.
For each of the following matrices, compute the determinants of all the leading principal submatrices and use them to determine whether the matrix is positive definite: (a) \(\left(\begin{array}{rr}2 & -1 \\ -1 & 2\end{array}\right)\) (b) \(\left(\begin{array}{ll}3 & 4 \\ 4 & 2\end{array}\right)\) (c) \(\left(\begin{array}{rrr}6 & 4 & -2 \\ 4 & 5 & 3 \\ -2 & 3 & 6\end{array}\right)\) (d) \(\left(\begin{array}{rrr}4 & 2 & 1 \\ 2 & 3 & -2 \\ 1 & -2 & 5\end{array}\right)\)
Show that if a matrix \(U\) is both unitary and Hermitian, then any eigenvalue of \(U\) must equal either 1 or -1
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