Determining initial and final states from FA diagram

I am new to automata. And learning to find concatenation of two FAs. But this one has confused me
FA 1
FA 2

I know how to do concatenation but I am confused that in FA 1, what does x1 means? Is it mean final state or does it mean both initial and final state because it is on the start?? Just clear me on this that what is initial state and what is final state in FA 1? Then I’ll take it from here and will be able to do concatenation.

P.S I know that +- in a state mean both initial and final state but I don’t know about double circle form. Kindly help me on this.


In your diagrams, a triangle points at the initial state, and double circles indicate final states. Inside the circles you can find the state names, such as x1.

Source : Link , Question Author : Tom , Answer Author : Yuval Filmus

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