Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2011/paper-2/14/b/i/solution

The transpose reverses product order, so . If is an orthogonal matrix, then and the given identity becomes
Multiply on the left by to obtain . Therefore is antisymmetric, so it is an antisymmetric matrix, namely .

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