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Subgroups, cosets and Lagrange's theorem

Why the order of a subgroup divides the order of the group.

Cosets of a subgroup H tile the group in equal-sized pieces, so |H| divides |G|. Picture it: the integers mod 12 as a clock; the subgroup {0, 4, 8} and its three cosets colour the clock in three colours. Think it: Lagrange is the reason element orders divide group orders, hence the reason RSA works.

Apstrādāts piemērs · divisors of 12

Divisors of 12

12

Solis pēc kārtas

  1. 12 = 2^{2} \times 3

    Prime-factorise first.

  2. d(n) = (2+1) \cdot (1+1) = 6

    Each divisor picks an exponent from 0 up to the prime's exponent, so multiply (exponent + 1) for each prime.

  3. 1, 2, 3, 4, 6, 12

    List them in increasing order.

Atbildēt uz šo jautājumu
1, 2, 3, 4, 6, 12

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Kā lietot: Subgroups, cosets and Lagrange's theorem

  1. Prime-factorise first.
  2. Each divisor picks an exponent from 0 up to the prime's exponent, so multiply (exponent + 1) for each prime.
  3. List them in increasing order.

Jautājumi, ko cilvēki vaicā

What is a group, in plain words?

A set with one operation that is associative, has an identity, and lets every element be undone. Symmetries of any object form a group. That is where the idea came from.

What is the difference between a ring and a field?

A ring has addition and multiplication that behave like the integers (you cannot always divide); a field is a ring where every non-zero element has a reciprocal, like the rationals or the reals.

Vairāk Abstract Algebra