MadeEasy WorkBook: Theory of Computation - Regular Expression

Question

Given answer is option c. Can anyone tell me how? 

Comments

can you please type the question instead of screenshot !

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But why? I think putting an image is more efficient than writing the question,as it is less prone to human errors. What problem do you have with it?

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this site has more number of questions, and all the test series and work book questions have high probability to be asked previously, then how one can find duplicates?

 

as it is less prone to human errors

as per my knowledge, typing a small question doesn't effect this much !!

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I have checked and didn't find any duplicate, that's why posted the question.

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And next time when someone else asks the same questions they will also not find since you've uploaded image instead of typing the question . I too used to do the same but it's better for the community if you can type questions

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OK @shaz

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@Jyoti Kumari97

https://gateoverflow.in/blog/5823/screenshot

Answer 1

C is the right answer.

 The  language L=(a+$\epsilon$)(bb*a)* can not produce b, bb

option a)  It says language L must contain all strings that does not have aa as substring so string b should be in L.

option b) It says no two consecutive a's again failed due to above string.

option c) This is is correct because L contains all strings that does not end with b and does not contain two or more consecutive a's.

Answer 2

You can try generating the strings first and see the pattern and eliminate the options.

The regular expression has the language L = { ε , a,ba,bba, aba, abba...}

You can see that we can't get the string "abab" using this, this alone eliminates options A and B.

And thus by generating more strings you can see that the correct option is indeed C.