# Automata Theory Questions and Answers – Regular Language & Expression – 1

This set of Automata Theory Multiple Choice Questions & Answers (MCQs) focuses on “Regular Language & Expression”.

1. A regular language over an alphabet a is one that can be obtained from
a) union
b) concatenation
c) kleene
d) All of the mentioned

Explanation: None.

2. Regular expression {0,1} is equivalent to
a) 0 U 1
b) 0 / 1
c) 0 + 1
d) All of the mentioned

Explanation: All are equivalent to union operation.

3. Precedence of regular expression in decreasing order is
a) * , . , +
b) . , * , +
c) . , + , *
d) + , a , *

Explanation: None.

4. Regular expression Φ* is equivalent to
a) ϵ
b) Φ
c) 0
d) 1

Explanation: None.

5. a? is equivalent to
a) a
b) a+Φ
c) a+ϵ
d) wrong expression

Explanation: Zero or one time repetition of previous character .
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6. ϵL is equivalent to
a) ϵ
b) Φ
c) L
d) Φϵ

Explanation: None.

7. (a+b)* is equivalent to
a) b*a*
b) (a*b*)*
c) a*b*
d) none of the mentioned

Explanation: None.

8. ΦL is equivalent to
a) LΦ & Φ
b) Φ & L
c) L & L
d) ϵ & L

Explanation: None.

9. Which of the following pair of regular expression are not equivalent?
a) 1(01)* and (10)*1
b) x(xx)* and (xx)*x
c) (ab)* and a*b*
d) x+ and x*x+

Explanation: (ab)*=(a*b*)*.

10. Consider following regular expression
i) (a/b)* ii) (a*/b*)* iii) ((ϵ/a)b*)*
Which of the following statements is correct
a) i,ii are equal and ii,iii are not
b) i,ii are equal and i,iii are not
c) ii,iii are equal and i,ii are not
d) all are equal

Explanation: All are equivalent to (a+b)*.

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