Q$2)($Total $15$ Points$)$

Construct a regular expression defining each of the

following languages over the alphabet $=\{a,b\}$ :

a$)$ All strings that end in a double letter. $(3$ Points$)$

b$)$ All strings that do not end in a double letter. $(3$ Points$)$

c$)$ All strings that have exactly one double letter in them. $(3$

Points$)$

d$)$ All words in which the letter $b$ is never tripled. This

means that no word contains the substring bbb$.(3$

Points$)$

e$)$ All words in which a is tripled or b is tripled, but not

both. This means each word contains the substring aaa

or the substring bbb but not both. $(3$ Points$)$