REGULAR EXPRESSION

1. Write regular expression for All the words of a language with alphabets {a,b,c}  that begins with an ‘a’ or a ‘c’ and then followed by some number of b’s.

•  (a+c)b

•  ((a+c)b)*

•  ((a+c)*b)*

•  (a+c)b*

2. Write regular expression for all the words of a language with alphabets {a,b}  that contains all the strings of a’s and b’s of length exactly three.

• (a+b)3

• (a3+b3)

• (3a+3b)

• (a+b)

3. Write regular expression for All the words of a language with alphabets {a,b}  that  begin with a and end with b

• = ab(a+b)*ab

• = a*(a+b)* b*

• a(a+b)* b

• = a(a+b) b

4.      Write regular expression for all the words of a language with alphabets {a,b}  that begin with a

• a (a+b)*

• a* (a+b)*

• a (a+b)

• a (a*+b*)*

5.      Write regular expression for all the words of a language with alphabets {a,b}  that ends with aa

• (a+b)* a*a

• aa

• (a+b) aa

• (a+b)* aa

6.      Write regular expression for all the words of a language with alphabets {a,b}  that have atleast one a

• (a+b)a(a+b)

• (a+b)* a (a+b)*

• (a+b)* a* (a+b)*

• (a+b)* a

7.      Write regular expression for all the words of a language with alphabets {a,b}  that have atleast one a and one b

• (a+b)* a (a+b)* b (a+b)*  + (a+b)*b (a+b)* a (a+b)*

• (a+b)* a (a+b)* b (a+b)* 

• (a+b)*b (a+b)* a (a+b)*

• (a+b)* a* (a+b)* b* (a+b)*  + (a+b)*b* (a+b)* a* (a+b)*

8.      Write regular expression for all the words of a language with alphabets {a,b}  that containing any number of a’s and b’s except null string.

• (a+b)^*

• (a+b)⁺

• (a+b)

• (a*+b*)

9.      Write regular expression for all the words of a language with alphabets {a,b}  that have the total number of a’s are divisible by 3

• (b*a*b*a*b*a*b*)*

• (b*(a+b)*(a+b)*(a+b*)*

• (b*ab*ab*ab*)*

• ((a+b)(a+b)(a+b))*

10.      Write regular expression for all the words of a language with alphabets {a,b}  that third character from right end of the string is always a.

• (a+b)*a (a+b)* (a+b)*

• (a+b)*a (a+b) (a+b)

• (a+b)*a (a*+b*) (a+b)

• (a+b)*a (a+b) (a*+b*)