Definition. Let X be a topological space and suppose xo is a point in X. A map exo : [0, 1] → X that sends every point of [0, 1] to the single point x, is called a constant path. Theorem 12.7. Let a be a path from x, to x1. Then ex, · a ~ a and a · ex, ~ a. To prove the above theorem, you will want to construct homotopies that demon- strate the equivalences. Recalling the definition of the product, notice that ex,' a is a path that sits still at x, while s runs from 0 to 1/2 and then moves along a (twice as fast as usual) while s runs from 1/2 to 1. To write down a homotopy, it may help to think about what the intermediate paths might look like between this and a. You'll have many choices, so you might as well choose a homotopy that is easy to write down. If we think of a as tracing out a path, then tracing out that same image in reverse yields a natural inverse.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
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Chapter10: Sequences, Series, And Probability
Section10.7: Distinguishable Permutations And Combinations
Problem 30E
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Could you explain how to do 12.7 with detailed explanation? Thank you!

Definition. Let X be a topological space and suppose x, is a point in X. A map exo :
[0, 1] → X that sends every point of [0, 1] to the single point x, is called a constant
path.
Theorem 12.7. Let a be a path from x, to x1. Then ex · a ~ a and a · ex, ~ a.
To prove the above theorem, you will want to construct homotopies that demon-
strate the equivalences. Recalling the definition of the product, notice that ex, · a is
a path that sits still at xo while s runs from 0 to 1/2 and then moves along a (twice
as fast as usual) while s runs from 1/2 to 1. To write down a homotopy, it may help
to think about what the intermediate paths might look like between this and a. You'll
have many choices, so you might as well choose a homotopy that is easy to write down.
If we think of a as tracing out a path, then tracing out that same image in reverse
yields a natural inverse.
Transcribed Image Text:Definition. Let X be a topological space and suppose x, is a point in X. A map exo : [0, 1] → X that sends every point of [0, 1] to the single point x, is called a constant path. Theorem 12.7. Let a be a path from x, to x1. Then ex · a ~ a and a · ex, ~ a. To prove the above theorem, you will want to construct homotopies that demon- strate the equivalences. Recalling the definition of the product, notice that ex, · a is a path that sits still at xo while s runs from 0 to 1/2 and then moves along a (twice as fast as usual) while s runs from 1/2 to 1. To write down a homotopy, it may help to think about what the intermediate paths might look like between this and a. You'll have many choices, so you might as well choose a homotopy that is easy to write down. If we think of a as tracing out a path, then tracing out that same image in reverse yields a natural inverse.
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