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¦b©ñÃP³o¨Ç±ø¥ó®É¡A¨Ò¦p¡A°²³]ª½¤Ø¥i¥H¨è¹º¡A¤Tµ¥¤À¨¤°ÝÃD´N¥i¥H¶i¦æ¤F¡C¦³Ãö³oÃþÅܤơA½Ð°Ñ¦Ò F. Klein,¡mFamous Problems of elementary geometry¡n¡C
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°á¹L©â¶H¥N¼Æªº¤H¥i¯à¹ï§Ú­Ì¦b³oùتº¡uÅé¡vªº©w¸qı±o¤£°÷¤@¯ë©Ê¡C¦b©â¶H¥N¼Æ¤¤¡A¡uÅé¡v¬O¨ã¦³¥[ªk»P­¼ªk¨âºØ¹Bºâªº¥N¼ÆÅé¨t¡A³o¨âºØ¹Bºâ¨ã¦³¬Y¨Ç¯S®íªº©Ê½è¡C§Ú­Ì¦b³oùص¹ªº©w¸q¡A¨ä¹ê¬O½Æ¼ÆÅ餧¤ºªº¤lÅé (subfields) ªº©wÅé¡C¾ú¥v¤W¨Ó¬Ý¡A³oºØ©w¸q©Î¤U¤@­Ó©w¸q $U(u_1 , \cdots , u_n)$ ´N¬O Kronecker ©Ò¿×ªº¡udomains of rationality¡v¡A³o¬O¼Æ¾Ç®a³Ì¥ýÁA¸Ñªº¡uÅé¡v¡C
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­nÃÒ©ú $\mathbf{Q}(\sqrt[3]{2})=$ $\mathbf{Q}+\mathbf{Q}\sqrt[4]{2}+\mathbf{Q}\sqrt{2}+\mathbf{Q}\sqrt[4]{8}$ §Ú­Ì¥u­n¯à°÷§â¤À¥À¦³²z¤Æ§Y¥i¡C¨ãÅ骺»¡¡A¹ï©ó¥ô·Nªº¦h¶µ¦¡

\begin{displaymath}g(t)\in\mathbf{Q}[t]\end{displaymath}

¥u­n $g(\sqrt[4]{2})\neq 0$¡A§Ú­Ì³£­n¦³¿ìªk§â $\frac{1}{g(\sqrt[4]{2})}$ Åܦ¨ $a+b\sqrt[4]{2}+c\sqrt{2}+d\sqrt[4]{8}$ ªº§Î¦¡,¨ä¤¤ a,b,c,d ¬O¦³²z¼Æ¡C¦]¬° f(t)=t4-2 ¬O Q ¤Wªº¤£¥i¬ù¦h¶µ¦¡¡A¥B f(t) »P g(t) ¤¬½è¡]§_«h f(t) ¬O g(t) ªº¦]¦¡¡A $f(\sqrt[4]{2})=0$ ¬G $g(\sqrt[4]{2})=0$¡^¡A¬G¥i§ä¨ì¦h¶µ¦¡ $\phi(t)$ »P $\psi(t)$¡A¨Ï $\phi(t)f(t)+\psi(t)g(t)=1$ ¥H $t=\sqrt[4]{2}$ ¥N¤J¡A±o

\begin{displaymath}\frac{1}{g(\sqrt[4]{2})}=\psi(\sqrt[4]{2})\end{displaymath}

§Q¥Î $(\sqrt[4]{2})^4=2$ ªºÃö«Y¡A¥i¥H§â $\psi(\sqrt[4]{2})$ ¤Æ¦¨

\begin{displaymath}a+b\sqrt[4]{2}+c\sqrt{2}+d\sqrt[4]{8}\end{displaymath}

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¥O $\alpha=\frac{1}{2}$¡A½ÐŪªÌÃÒ©ú $4t^3-3t-\frac{1}{2}$ ¬OQ ¤Wªº¤£¥i¬ù¦h¶µ¦¡¡C
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­Y £\ »P £] ¬O¥N¼Æ¼Æ¡A«h

\begin{displaymath}[\mathbf{Q}(\alpha , \beta):\mathbf{Q}]<\infty\end{displaymath}

¤µ $\alpha+\beta$, $\alpha\beta$ $\in\mathbf{Q}(\alpha , \beta)$ ¬G

\begin{displaymath}1 , \alpha+\beta , (\alpha+\beta)^2 , \cdots , (\alpha+\beta)^n\end{displaymath}

¥²©w¦b Q ¤W½u©Ê¬Û¨Ì¡A¨ä¤¤ n ¬O¬Y­Ó¥¿¾ã¼Æ¡C¦]¦¹ $\alpha+\beta$ ¬O¥N¼Æ¼Æ¡C©ÎªÌ¡A¥O

\begin{displaymath}f(t) , g(t)\in\mathbf{Q}[t]\end{displaymath}

¥B $f(\alpha)=0$,$g(\beta)=0$ ¥O $\alpha=\alpha_1$,$\alpha_2$,¡K,$\alpha_n$ ¬O f(t)=0 ªº n ­Ó®Ú¡A¦Ò¼{

\begin{displaymath}h(t)=g(t-\alpha_1)g(t-\alpha_2)\cdots g(t-\alpha_n)\end{displaymath}

«h $h(\alpha+\beta)=0$¡A«h h(t) ªº«Y¼Æ¬O$\alpha_1$,$\alpha_2$,¡K,$\alpha_n$ ªº¹ïºÙ¦h¶µ¦¡¡A¬G $h(t)\in\mathbf{Q}[t]$¡C¦P²z½ÐŪªÌÃÒ©ú $\alpha\beta$ ¤]¬O¥N¼Æ¼Æ¡C
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¦³¤@¬q´¡¦±¡CKlein ´¿¥D«ù·í®É¤@®M¡m¼Æ¾Ç¦Ê¬ì¥þ®Ñ¡n(Enzykiopädie der mathematische Wissensenschaften) ªº½s¿è¤u§@¡C¥LÀÀ©w³\¦h¥DÃD¡A¦AÁܽгo¨Ç¥DÃDªº±M®a¼g§@¡C¨ä¤¤¤@­Ó¥DÃD´N¬O­n¤¶²ÐÃþ¦ü Feuerbach ©w²z³oºØªìµ¥´X¦óªºµ²ªG¡CKlien ÁܽРMax Simmon ¼g³o­Ó¥DÃD¡C·í Simmon ¼g¦n¤§«á¡AKlein §ïÅÜ¥D·N¤F¡A¥L©Úµ´¥Zµn³o­Ó¥DÃD¡CKlein »{¬°¡A¹³¡m¼Æ¾Ç¦Ê¬ì¥þ®Ñ¡n¦p¦¹ÄYÂÔªº¬ì¾Ç½×µÛ¡A¬O¤£®e³\³oÃþªìµ¥´X¦ó¦³¥ô¦ó¥ß¨¬ªº¦a¤è¡C¦]¦¹¡ASimmon ¥u¦n¦Û¤v¥Xª©¥Lªº½×¤å¡A§Y M. Simmon,¡qUber Entwicklung der Elementargeometrie in XIX Jahrhundert¡r, 1906, Berlin.
   


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