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Homework Help: Determine whether this is a subfield of R

  1. Mar 1, 2008 #1
    Let Q denote the field of rational numbers and R denote the field of real numbers. Determine whether or not set S = {r + s√2 | r, s € Q} is a subfield of R.
     
    Last edited: Mar 1, 2008
  2. jcsd
  3. Mar 1, 2008 #2

    Dick

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    Belong to quotient of what? That's not very grammatical.
     
  4. Mar 1, 2008 #3
    Let Q denote the field of rational numbers and R denote the field of real numbers. Determine whether or not set S = {r + s√2 | r, s € Q} is a subfield of R.
     
  5. Mar 2, 2008 #4

    Dick

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    That's better. Just show S is closed under the field axioms. The big question is if a and b are in S is a/b in S? If b=r+sqrt(2)s it's useful to multiply the numerator and denominator of a/b by (r-sqrt(2)s).
     
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