Exercise · ZW-INVERSE-MATRIX-009 · ★★★ Advanced
Select all values of \(k\) for which \(\begin{pmatrix}k & 2\\ 8 & k\end{pmatrix}\) is NOT invertible.
Select all correct answers.
Show answer
- A. \(k=4\)
- B. \(k=-4\)
Explanation
It is not invertible exactly when its determinant is zero: \(k^2-16=0\), that is \(k=4\) or \(k=-4\). For \(k=0\) the determinant is \(-16\) and for \(k=2\) it is \(-12\).
Review the concept: Inverse matrix
The inverse of a square matrix \(A\) is the matrix \(A^{-1}\) that gives the identity \(I\) when multiplied by \(A\) on either side; if it exists, \(A\) is called invertible.
\[AA^{-1}=A^{-1}A=I\]
More practice problems: inverse matrix
- ZW-INVERSE-MATRIX-001 Compute the inverse of [2 1; 5 3].
- ZW-INVERSE-MATRIX-002 Which of these matrices has NO inverse?
- ZW-INVERSE-MATRIX-003 Compute the inverse of the diagonal matrix [2 0 0; 0 -4 0; 0 0 5].
- ZW-INVERSE-MATRIX-004 If A and B are invertible matrices of the same size, what is (AB)^-1?
- ZW-INVERSE-MATRIX-005 Solve Ax=b using the inverse, with A=[1 2; 3 5] and b=(1,2)^T.
- ZW-INVERSE-MATRIX-006 A square matrix A satisfies A^2-3A+I=0. Which expression is A^-1?
- ZW-INVERSE-MATRIX-007 Let A=[1 2 0; 0 1 3; 0 0 1]. What is the entry in row 1, column 3 of A^-1?
- ZW-INVERSE-MATRIX-008 If A is an invertible 2×2 matrix, what is (3A)^-1?