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Simple Field Extension Question

  1. Apr 2, 2009 #1
    I'm currently trying to prove that (for a field extension [itex]K[/itex] of the field [itex]F[/itex]) if [itex]u\in K[/itex] and [itex]u^2[/itex] is algebraic over [itex]F[/itex] then [itex]u[/itex] is algebraic over [itex]K[/itex].

    I thought of trying to prove it as contrapositive but that got me nowhere--it seems so simple but I don't know what to use for this. Any help with this would be greatly appreciated.
  2. jcsd
  3. Apr 2, 2009 #2
    Well clearly u is algebraic over K (it is an elemnt of K) so I'm guessing you mean to say that u is algebraic over F. Well if u^2 is algebraic over F then let f be a polynomial in F[x] such that f(u^2)=0. I don't want to give it away but if you think about the polynomial f(x^2)...
  4. Apr 2, 2009 #3
    Oh wow yea, ok it's pretty clear. I think I was complicating things. Thanks.
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