regular expression

Question

Comments

Your answer is correct,it is mistake from their side.

FYI,this is highest asked question in gatecse fb group

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Answer 1

Let us see how we can rewrite the expression in the question :

Given , R.E.  =  ( a + b )* ( a + b + ϵ ) a

                    =  ( ϵ + a  + b )*  ( a + b + ϵ ) a   [As ϵ is already there in (a + b)* so problem in adding ϵ to 1st term]

                    =  ( ϵ + a + b )⁺ a

                    =  ( ϵ + a + b* )⁺ a  [No problem in writing this step bcoz in b* there is already an ϵ to account for and rest all combinations of b* will be covered by b itself as it is within the Kleene's Closure..

Hence B) is the correct answer..