Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2003/iii/paper-26/5/b/solution

Identify the ambient Euclidean space with and let be multiplication by . Equivalently, in real coordinates,
This linear map preserves the norm and satisfies . On the unit sphere define
It is continuous, tangent because it lies in , and has norm one everywhere. It is therefore a nowhere-zero section of the tangent bundle, including when and the sphere is . This supplies a nonvanishing tangent field on an odd-dimensional sphere explicitly.

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