I don't understand how to do these at all. Can someone help and or give me some reference material?

For each of the REs below, find the shortest string in the corresponding language that is not in the language of the other two REs, and explain in the simplest way possible why it's not in the other two. (a) R,-(bb U b)* U (ba U a)" (b) R2 (ba)* (ab)* (c) R3 (ab U aba)*a* Example: "a" is not in L2 because all string in L2 have even length. Problem 3. Are the following statements true or false? In each case, justify your answer, using the appropriate definitions of strings, sets, languages, regular operations, etc Be as precise and brief as possible. (a) the union of 0 1* and 1*0* equals (1 U 0)* (0 U 1) (b) the intersection of 0*1 and 10* is empty (c) abcd is in (a (cd)* b)* Problem 4. For the languages (b) and (c) in Problem 1, find the FSA that accepts it. Try to make it as simple as possible. Show your FSA both as a diagram and as a table