Problems on Cyclotomic Extensions 1, Determine all of the subfields of $\mathbb{Q}_{12} $. 2, Show that $\cos (\pi/9) $ is algebraic over $\mathbb{Q} $, and find $[\mathbb{Q}(\cos (\pi/9)):\mathbb{Q}] $. 3, Show that $\mathbb{Q}(\cos (2\pi/n)) $ is Galois over $\mathbb{Q} $ for any $n $. Is the same true for $\mathbb{Q}(\sin (2\pi/n)) $? 4, Show that $\cos (2\pi/n) $ and $\sin (2\pi/n) $ are algebraic over $\mathbb{Q} $ for any $n $. |
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5, If n is odd, prove that $\mathbb{Q}_{2n}=\mathbb{Q}_n $. 6, Let n,m be poisitive integers with d=gcd(m,n) and l=lcm(m,n). a)If n divides m, prove that $\mathbb{Q}_n\subset\mathbb{Q}_m $. b)Prove that $\mathbb{Q}_n\mathbb{Q}_m=\mathbb{Q}_l $. c)Prove that $\mathbb{Q}_m\cap\mathbb{Q}_n=\mathbb{Q}_d $. |
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