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.