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Which of the following regular expression corresponds to the language of all strings over the alphabet {a, b) that contains exactly two a’s

(i) aa

(ii) ab*a

(iii) b* ab*a

  • a)
    (i) arid (ii) only

  • b)
    None of these.

  • c)
    (i) and (iii) only

  • d)
    (ii) and (iii) only

Correct answer is option 'D'. Can you explain this answer?
Verified Answer
Which of the following regular expression corresponds to the language ...
Explanation:

A regular expression describes the language over some alphabet.

(i) aa: This regular expression matches the strings "aa" only. It does not cover the cases where there are b's in between or around the a's. So, it does not represent all strings over the alphabet {a, b} that contains exactly two a’s.

(ii) ab*a: This regular expression matches strings like "aa", "aba", "abba", etc. It allows for zero or more b's between two a's and hence, it corresponds to the language of all strings over the alphabet {a, b} that contains exactly two a’s.

(iii) b*ab*a: This regular expression matches strings like "aa", "aba", "abba", "baa", "baba", etc. It allows for zero or more b's before, between, and after two a's and hence, it corresponds to the language of all strings over the alphabet {a, b} that contains exactly two a’s.


Therefore, only (ii) and (iii) correctly represent the language of all strings over the alphabet {a, b} that contains exactly two a’s.


The correct answer is  (ii) and (iii) only.

 
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Most Upvoted Answer
Which of the following regular expression corresponds to the language ...
The regular expression that corresponds to the language of all strings over the alphabet {a, b} that contains exactly two "a"s is:

b*ab*a*b*
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Community Answer
Which of the following regular expression corresponds to the language ...
We cannot generate abab using 2nd and 3rd option .then how is it correct? please explain .
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