In: Advanced Math
Prove that each element in Pentagon D5 has a unique inverse under the binary operation.
D5={AF, BF, CF, DF, EF,0,72,144,216,288}
Solution:
Set of symmetries of an regular pentagon with vertices levelled as
in anticlockwise order. There are
rotations
(
) where
means rotation about
degrees and
reflections
(
)
where
means reflection about the vertices
.
Observe that
We can prove the statement through Cayley Table.
From the Cayley table one can say that the inverse element of
that is
, similarly
and
. Here from the Cayley table we conclude that each element of
has
unique inverse element. hence proved.