4.
ab ba
−1
o(ab) < ∞,
ba = a (ab)a, o(ab) = o(ba);
n n −1 n
o(ab) = ∞,
n, (ab) 6= 1, (ba) = (a aba) =
−1 n
a (ab) a 6= 1,
o(ba) = ∞.
5.
n > 2. G n
−1 −1
n > 2 o(a) = n, a 6= a , o(a ) = o(a) = n.
G
n
6.
n > 2 Z(Sn) = {e}.
9 π ∈ Z(Sn), π = 1, π
Æ
7.
Q+
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