Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2018/ii/paper-2/25i/b/solution

For a unit-speed curve with nonzero curvature of a space curve , define the Frenet frame
The torsion of a space curve is
with this choice of convention.
For the requested example, take the unit-speed circle
and the unit-speed circular helix
Both have the constant nonzero curvature , but their torsions are respectively and . A proper Euclidean motion of Euclidean three-space preserves torsion, so no such rigid motion relates the two curves.

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