Permutations Algebra: Solving Homework Problem

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SUMMARY

The discussion focuses on solving a permutation algebra problem involving the expression (1 3 4 9)^7(2 6 8)^7. The key conclusion is that the transformation from (1 3 4 9)^7 to (1 3 4 9)^{-1} is based on the property of permutation cycles, where the order of a cycle with n elements is n. Specifically, since (1 3 4 9) has an order of 4, raising it to the 7th power results in (1 3 4 9)^{-1}, as 7 is equivalent to -1 modulo 4. Conversely, (2 6 8) has an order of 3, and thus (2 6 8)^7 simplifies to (2 6 8)^1.

PREREQUISITES
  • Understanding of permutation cycles and their orders.
  • Familiarity with modular arithmetic in the context of group theory.
  • Knowledge of basic algebraic manipulation of permutations.
  • Experience with cycle notation in permutation algebra.
NEXT STEPS
  • Study the properties of permutation groups, focusing on cycle notation.
  • Learn about modular arithmetic and its applications in group theory.
  • Explore advanced topics in algebra, such as the structure of symmetric groups.
  • Practice solving permutation problems using different cycle orders and their implications.
USEFUL FOR

Students studying abstract algebra, particularly those focusing on group theory and permutation algebra. This discussion is beneficial for anyone tackling homework problems related to permutations and their properties.

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Homework Statement



This is a worked problem:

[PLAIN]http://img409.imageshack.us/img409/4821/14091194.gif


The Attempt at a Solution



In the answer, how did they get from (1 3 4 9)^7(2 6 8)^7 to (1 3 4 9)^{-1}(2 6 8)?

I know that \tau^7 means the permutation \tau repeated 7 times. But I just don't understand why they changed "7" to "-1" on the first cycle and changed "7" to "1" on the second. They are probably using a shortcut but I can't follow it... :confused:
 
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(1249) involves 4 numbers and so has order 4- that is (1249)^4= identity. It is generally true that a cycle with n numbers has order n (that is used in the first problem) because doing it n time just cycles through all the numbers. Of course (1249)^8= (1249)^4(1249)^4= identity and 7 is just 1 less than 8: (1249)^7= (1249)^-1 because (1249)^7(1249)= (1249)^8= identity.
 

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