About the Product of Two Commuting Elements

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SUMMARY

The discussion centers on finding an example of two commuting elements whose product does not have an order equal to the least common multiple of their individual orders. The user initially considers the elements -1 and 1 in the integers, where the product yields an order of 1, while both elements have infinite order. However, a more suitable example is suggested using the group of integers modulo 12, specifically the group (ℤ/12ℤ, +), which illustrates the concept more clearly.

PREREQUISITES
  • Understanding of group theory and the concept of commuting elements
  • Familiarity with the order of elements in a group
  • Knowledge of least common multiples in mathematical contexts
  • Basic understanding of modular arithmetic, particularly ℤ/12ℤ
NEXT STEPS
  • Study the properties of group theory, focusing on commuting elements
  • Learn about the order of elements in various algebraic structures
  • Explore modular arithmetic and its applications in group theory
  • Investigate examples of groups where the product of elements does not follow the least common multiple rule
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Mathematics students, particularly those studying abstract algebra, educators teaching group theory concepts, and anyone interested in the properties of algebraic structures.

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Homework Statement


I am asked to offer an example of two commuting elements whose product does not have an order equal to the least common multiple of their individual orders.

Homework Equations

The Attempt at a Solution


Consider ##-1## and ##1## in ##\mathbb{Z}##. Then ##1+(-1) = 0## which has an order of ##1##, but the order of ##-1## and ##1## is infinity.

Would this be an acceptable answer? I find it unsettling for some reason, but I cannot see anything wrong with it.
 
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This looks a bit like cheating. What is the least common multiple of ##\infty## and ##\infty##?
You should consider ##( \mathbb{Z_{12}}\, , \,+) = (\mathbb{Z}/12 \mathbb{Z} \, , \, +)## instead, i.e. the remainders from division by ##12## or simply the little hand on the clock.
 

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