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Plane Geometry - Bruce E. Shapiro

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SECTION 52. ARC LENGTH 311where we have introduced the symbol ÃB to represent an arc of a greatcircle,and where r = 1 is the radius of the sphere. ThusL(γ) ≥ L(ÃB)We have proven the following theorem.Theorem 52.4 The path of shortest distance, on the surface of a sphere,between two points A and B on the surface of the sphere, lies along a greatcircle connecting the two points. More specifically, if γ(t) : [a, b] ↦→ S is anycurve on on the sphere such that γ(a) = A and γ(b) = B thenL(γ) ≥ L(ÃB)Figure 52.3: The arc of the great circle from A to B is shorter than anyother curve on the surface of the sphere connecting A to B.γ(t)Therefore we will make the following assumption: a line in spherical geometrycorresponds to the arc of a great circle connecting the two points.Revised: 18 Nov 2012 « CC BY-NC-ND 3.0.

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