Make a regular expression that accept all strings containing b symbol in even number of time (∑ = {a,b})?

Question

explain it step by step!

Answer 1

To make sure that the number of bs are even, just ensure that you have any number of as (incl 0), followed by a b, any number of as, another b. Repeat any number of times (incl 0) and since there are exactly 2 bs in the group, there will be an even number in the result. You must also include some as at the end:

(a*ba*b)*a*

Answer 2

Not sure whether if I understand you question correctly, but I assume the following is the thing you're looking for,

To express the following, and indicate b always happen at even number of time, says,
{a,b,c,b,d,b,e,b,....}

that, the expression will be
N2i=b, where i = 1, 2, 3.... (integer)

note: 2i is the subcript at bottom of N. can't format it here.

Answer 3

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