Question

Find a regular expression that defines teh lang consisting of all strings of a's and b's in which the third character from teh end is a b

Answer 1

*(a|b)(a|b)(a|b)
the third last character is (a|b) right??

Answer 2

noo the third last character must be a b

Answer 3

lol ... a or b ??

Answer 4

ohh a "b" hahahah i see ur confusion

Answer 5

*b(a|b)(a|b) if b
*a(a|b)(a|b) if a

Answer 6

well like what do u think abt this one
a*b*bab?

Answer 7

it says it should begin with 'a'
at some unknown point it must be b
and the third last is b
second last is a
last is b

Answer 8

righhht so that is correct to right? i mean there can be mannnnyyy answers

Answer 9

yes .. this is one of the right answer.
*b(a|b)(a|b) is the general pattern

Answer 10

well if u use a|b then its either or b may not neccesarily be the 3 rd last letter

Answer 11

use \( \large \color{Red} b \) in third last place
use \( \large \color{Red} {(a|b)} \) in second last place
use \( \large \color{Red} {(a|b)} \) in last place

Answer 12

haha i am getting confused with all teh a's and b's hahhaah

Answer 13

Couldn't you have more than 3 characters?

Answer 14

As in, shouldn't abbabaabaabbbababaa be a valid expression?

Answer 15

ya y not i mean like i am assuming there can be mannnnnny answerrrsss

Answer 16

Well it seems like you could do something like \[\begin{matrix}(a|b)(a|b)(a|b)....(a|b)(b)(a|b)(a|b)\end{matrix}\]

Answer 17

okkkk yaaaaa i seeee that okkkk