Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2026/iii/paper-115/1/c/solution

On the unit sphere choose the outward unit normal . For tangent vector fields ,
so
If are orthonormal, the Gauss equation gives
Thus the round unit sphere has sectional curvature one. Tracing over an orthonormal basis gives its scalar curvature

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