 Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2017/digital-systems-linear-algebra-introduction-to-formal-proof/5/a/i/solution

E = 001010100, E^{- 1} = E .

Left multiplication exchanges the two rows. Applying the same exchange twice restores every row, so

E^{2} = I_{3}

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