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: Abstract Algebra: Ring Proof (Multiplicative Inverse)

  1. Feb 5, 2016 #1


    User Avatar
    Gold Member

    1. The problem statement, all variables and given/known data
    Suppose R is a commutative ring with only a finite number of elements and no zero divisors. Show that R is a field.

    2. Relevant equations

    Unit is an element in R which has a multiplicative inverse. If s∈R with r*s = 1.
    A zero divisor is an element r∈R such that there exists s∈R and rs = 0 (or sr = 0).

    3. The attempt at a solution

    1. Since R is a commutative ring, we only need to prove one axiom, that is that it satisfies the multiplicative inverse for all values in R.
    2. I have a theorem that we just went over that states:
    Theorem: If R is a finite ring, then for all r ∈ R, r is either a unit or a zero divisor.
    3. Since the question states that there is no zero divisors in this finite ring, we can use the theorem to state that they must all be units.
    4. Noting that they are all units means they all have the stipulation that x*s = 1. Meaning they all have a multiplicative inverse.

    Proof is done.

    Is this a complete proof?
  2. jcsd
  3. Feb 6, 2016 #2


    User Avatar
    Science Advisor
    Homework Helper

    Yes. If I were in a pedantic mood, I could remark that you should exclude 0 in some statements.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted