GATE | GATE CS Mock 2018 | Set 2 | Question 48

What is the language generated by this regular expression ?

(b + ε ) (a + ab)* 

(A) Always starts with b
(B) Can have any number of ba and ab
(C) Can not have 2 b’s together.
(D) Starts and end with same symbol


Answer: (C)

Explanation:

R.E. = b(a + ab)* + (a + ba)*
     = (b + ε ) (a + ab)* 

Or

R.E. = (a + ba)* + (a + ba)*b
     = (a + ba)* (ε + b)

Both means ‘Can not have 2 b’s together’.
Option (C) is Correct.

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