 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-oxford/2023/prelims/mathematics-i/5/a/iii/solution

The identity is the identity matrix

e = h (0, 0, 0) = I_{3} = 100010001 .

Left or right matrix multiplication by it preserves every entry, as is also immediate from the product formula above.

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