Big Ideas Math Integrated I, 2016
BI
Big Ideas Math Integrated I, 2016 View details
2. Parallel Lines and Transversals
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Exercise 20 Page 508

Can you define parallel lines in spherical geometry?

No, see solution.

Practice makes perfect

Let's recall the definition of a line in spherical geometry.

A line is a circle on the sphere whose diameter is equal to the diameter of the sphere.

With the above definition, we can draw a sphere and a line in spherical geometry.

Sphere.png

Can we draw two parallel lines in a sphere? No, we cannot. The reason is that this line would have to be offset either up or down to be parallel, and therefore it will not have the same diameter as the sphere.

Sphere2.png

This means it would not meet the definition of a line in spherical geometry anymore. Therefore, since we cannot have parallel lines in a sphere, we cannot have a transversal that intersects two parallel lines.