Friday, 3 January 2014

field theory - If $L_1/K$ and $L_2/K$ are not Galois (solvable), then $L_1L_2/K$ is not Galois (solvable)

This is part of an exam preparation:




Prove/contradict:





  1. If $L_1/K$ and $L_2/K$ are not Galois, then $L_1L_2/K$ is not Galois.

  2. If $L_1/K$ and $L_2/K$ are not solvable Galois extensions, then $L_1L_2/K$ is not a solvable Galois extension.




For 1, I think that the answer is false. I thought of "splitting" the splitting field of a polynomial. For example, the splitting field of $X^3-2$ over $\mathbb{Q}$ is $\mathbb{Q}(2^{1/3},\omega)$ and then taking $\mathbb{Q}(2^{1/3})$ and $\mathbb{Q}(\omega)$. The problem is that $\mathbb{Q}(w)/\mathbb{Q}$ is Galois and I can't think of a different kinds of example.



For 2, I think that the answer is true. We have $$G_1 = Gal(L_1L_2/K) \leq Gal(L_1/K) \times Gal(L_2/K) = G_2$$




Then I thought of making some claim about a subgup of a solvable group but Im not really sure how to proceed.



Thanks.

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