Solution

Past exam of the mathematics course of the University of Cambridge / 2005 / ib / Paper 1 / 2A / Solution

Past exam of the mathematics course of the University of Cambridge / 2020 / ii / Paper 4 / 25I / c / Solution

A ring torus with major radius $R$ and minor radius $r<R$ has parametrization
$$
X(\theta,\phi)=((R+r\cos\theta)\cos\phi,(R+r\cos\theta)\sin\phi,r\sin\theta)
$$
and Gaussian curvature $K(\theta)=\cos\theta/[r(R+r\cos\theta)]$.

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 Incoming links: Ring torus