1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Can someone check this for me? (Equivalence classes)

  1. Oct 18, 2014 #1
    • This thread is missing the Homework Template due to originally being posted in another forum.
    Question: Find the equivalence classes and the number of equivalence classes of the following relations.

    A is the set of all possible strings of 3 or 4 letters in alphabet {A, B, C, D}, and (x, y) ∈ R if and only if x and y have the same first letter and the same third letter.

    My attempted answer: A_B_, A_C_, A_D_, B_A_, B_C_, B_D_, C_A_, C_B_, C_D_, D_A_, D_B_, D_C_.
    This would be 12 different classes.

    Is this correct or am I missing something?
  2. jcsd
  3. Oct 19, 2014 #2
    There is typically no restriction on strings containing repeat letters. Other than that, this looks fine.
  4. Oct 21, 2014 #3
    Awesome thanks :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted