Regular expression for your DFA will is (b + ab*a)*
The language description: Symbol b
can appear in any fashion but restriction is a
can to be for even number of times in language strings.
(b + ab*a)*
^ ^ ^
| | "* because loop on initial state"
| | "* on b because of self loop with label b on 2nd state"
|
|"+ because two outgoing edges, One is self loop other via 2nd state"
Here: + means Union, * means repetition for zero or more times
Note: Language string examples: {^, b, aa, bababb...}
(even a
s and any b
s including null)