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Exercise 104

Avg difficulty 4.0

Find all the xx that make the matrix inverse [121x]−1\begin{bmatrix} 1 & 2 \\ 1 & x \end{bmatrix}^{-1} have only integer entries (no fractions). Note that there are two answers.

Lebl, Notes on Diffy Qs, §10.6 Determinant, exercise 104

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Adapted from Notes on Diffy Qs © 2008–2026 Jiří Lebl. Licensed under CC BY-SA 4.0. Source: Notes on Diffy Qs: Differential Equations for Engineers. Imported at revision 658bcae.