- #1
Mandelbroth
- 611
- 24
This was an exercise out of Garling's A Course in Galois Theory.
Suppose ##L:K## is a field extension. If ##[L:K]## is prime, then ##L:K## is simple.
I've developed a habit of checking my work for these exercises religiously (the subject matter is gorgeously elegant, so I want to do it justice). I found a much more complicated answer than mine when I googled it, which makes me uncomfortable.
Here's my proof:
Suppose ##\alpha\in L## is not in ##K##. Because ##[L:K]=[L:K(\alpha)][K(\alpha):K]## and ##[K(\alpha):K]\neq 1##, we must have ##[K(\alpha):K]=[L:K]##. Because any two vector spaces with the same dimension over the same field are isomorphic, this completes the proof. []
Is this right?
Suppose ##L:K## is a field extension. If ##[L:K]## is prime, then ##L:K## is simple.
I've developed a habit of checking my work for these exercises religiously (the subject matter is gorgeously elegant, so I want to do it justice). I found a much more complicated answer than mine when I googled it, which makes me uncomfortable.
Here's my proof:
Suppose ##\alpha\in L## is not in ##K##. Because ##[L:K]=[L:K(\alpha)][K(\alpha):K]## and ##[K(\alpha):K]\neq 1##, we must have ##[K(\alpha):K]=[L:K]##. Because any two vector spaces with the same dimension over the same field are isomorphic, this completes the proof. []
Is this right?