Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2024/ib/paper-1/11e/ii/solution

Tangency along means
for every . Consequently is perpendicular to the first tangent plane exactly when it is perpendicular to the second. The ambient characterization of a geodesic therefore proves the tangency invariance of an ambient-surface geodesic:

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