Question

Find a regular expression for the following language over the alphabet Σ = {a,b}.

L = {strings that begin and end with a and contain bb}.

Answer 1

L = {Strings that begin and end with 'a' and contain 'bb'}

Strings :-abba, aabba, abbaa, aabbba, aaaabbbba, aabbbbbaa etc....

We need to find regular expression for the given language over the alphabet {a,b}

Regular Expression :- a(a+b)*bb(a+b)*a

From above solution here we have starts with 'a'

and next (a+b)* means it contains a or b

and next bb means it should contain bb in middle of the string.

and next we take (a+b)* as usual.

finally the string ends with a .

so the Final Regular expression for given language is : a(a+b)*bb(a+b)*a