# 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

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.

• x1 is just the name of a state. The triangle points at the initial state, and the final states are the ones with the double circle. – Yuval Filmus Dec 1 '18 at 21:47
• then x1 means both initial and final stage? @YuvalFilmus – Tom Dec 1 '18 at 21:50
• Yes, this seems to be the case according to what I wrote. – Yuval Filmus Dec 1 '18 at 21:50

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.