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Everything about Circle Group totally explained

In mathematics, the circle group, denoted by T (or in blackboard bold by mathbb T), is the multiplicative group of all complex numbers with absolute value 1, for example, the unit circle in the complex plane. » mathbb T = is equivalent to ho_n.

Algebraic structure

In this section we'll forget about the topological structure of the circle group and look only at its algebraic structure.
   The circle group T is a divisible group. Its torsion subgroup is given by the set of all nth roots of unity for all n, and is isomorphic to Q/Z. The structure theorem for divisible groups tells us that T is isomorphic to the direct sum of Q/Z with a number of copies of Q. The number of copies of Q must be c (the cardinality of the continuum) in order for the cardinality of the direct sum to be correct. But the direct sum of c copies of Q is isomorphic to R, as R is a vector space of dimension c over Q. Thus » mathbb T cong mathbb R oplus (mathbb Q / mathbb Z).,

The isomorphism » mathbb C^ imes cong mathbb R oplus (mathbb Q / mathbb Z)

can be proved in the same way, as C× is also a divisible abelian group whose torsion subgroup is the same as the torsion subgroup of T.

Further Information

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