Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2006/paper-1/2/a/i/solution

The characteristic polynomial is . Solving the three eigenvector equations gives
Each eigenspace consists of the scalar multiples of its displayed nonzero vector. Their pairwise dot products vanish: and . This also agrees with the orthogonal diagonalization of a real symmetric matrix.

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