next up previous
¤U¤@­¶: Zero Divisor ©M Unit ¤W¤@­¶: ªì¯Å Ring ªº©Ê½è «e¤@­¶: Ring ªº°ò¥»©w¸q

¥Ñ Ring ªº©w¸q©Ò±oªº©Ê½è

¦b³o¸`¤¤§Ú­Ì¤¶²Ð¤@¨Çª½±µ¥Î ring ªº©w¸q (¤×¨ä¬O¤À°t²v) ´N¥i±À±oªº°ò¥»©Ê½è.

­Y R ¬O¤@­Ó ring, ¨ä¥[ªkªº identity §Ú­Ì´¿¸g´£¹L²ßºD¤W¬O¥Î 0 ¨Óªí¥Ü. ÁöµM³o¤@­Ó 0 ¨Ã«D¤j®a¼ô±xªº¨º­Ó 0 ¤£¹L´N¦]¬°¥¦©M¤j®a¼ô±xªº 0 ¦³³h¦@³qªº©Ê½è, ©Ò¥H§Ú­Ì¥Î 0 ¨Óªí¥Ü¥¦. ­þ¨Ç¦@³qªº©Ê½è©O? °£¤F a + 0 = 0 »P a + x = a $ \Rightarrow$ x = 0 ¥ , ¥H¤Uªº Lemma ¤j®aÀ³¤]«Ü¼ô±x§a!

Lemma 5.2.1   ­Y R ¬O¤@­Ó ring ¥B 0 ¬O¨ä¥[ªkªº identity, «h¹ï¥ô·Nªº a $ \in$ R ¬Ò¦³

a . 0 = 0 . a = 0.

µý ©ú. ¤j®aÀ³¥i¥HÆ[¹î¥X 0 ¬O©M¥[ªk¦³Ãöªº, ¦Ó a . 0 ¤S©M­¼ªk¦³Ãö, ©Ò¥H¤£Ãø·Q¹³³o­Ó Lemma ¤@©w©M¤À°t²v¦³Ãö.

¥Ñ©ó 0 ¬O¥[ªkªº identity, ¬G¥Ñ (R3) ª¾ 0 + 0 = 0. ¦]¦¹¥Ñ (R8) ±o:

a . 0 = a . (0 + 0) = a . 0 + a . 0.

µM¦Ó¥Ñ (R3) ª¾: a . 0 + 0 = a . 0, ¤]´N¬O»¡ x = 0 ©M x = a . 0 ¬Ò¬° a . 0 + x = a . 0 ªº¸Ñ. ¬G§Q¥Î Lemma 5.1.2 (2) ¥iª¾ a . 0 = 0.

¦P²z§Q¥Î (0 + 0) . a = 0 . a ¥i±o 0 . a = 0. $ \qedsymbol$

Remark 5.2.2   ¦³ªº¦P¾Ç©Î³|§Q¥Î

a . 0 = a . (a - a) = a . a - a . a = 0 (5.1)

³o¤@­Óµ¥¦¡¨ÓÃÒ©ú Lemma 5.2.1. ¦¡¤l (5.1) ¨ä¹ê¬O¦³°ÝÃDªº. °ÝÃDµo¥Í¦b R ¤¤¨Ã¨S¦³ ¡u-¡v ³o¤@­Ó¹Bºâ. ´«¥y¸Ü»¡¤j®a²ßºD¼gªº 0 = a - a À³¸Ó¼g¦¨ 0 = a + (- a). ¦]¦¹¦¡¤l (5.1) À³¸Ó§ï¼g¦¨

a . 0 = a . (a + (- a)) = a . a + a . (- a).

µM¦Ó a . a + a . (- a) ·|µ¥©ó 0 ¶Ü? ­Y¬O 0 ´Nªí¥Ü a . (- a) À³¸Ó¬O a . a ªº¥[ªk inverse, ¤]´N¬O a . (- a) = - (a . a). ³o¤@ÂI¨ì¥Ø«e¬°¤î§Ú­ÌÁÙ¤£ª¾¹D¬O¹ïÁÙ¬O¿ù (¨£ Lemma 5.2.3). ©Ò¥H³o¨Ã¤£¯àÃÒ©ú Lemma 5.2.1.

¨ì©³§Ú­Ì¼ô±xªº a . (- a) = - (a . a) ¹ï¶Ü? ¤U¤@­Ó Lemma §i¶D§Ú­Ì¨ä¹ê¬O¹ïªº.

Lemma 5.2.3   ­Y R ¬O¤@­Ó ring, «h¹ï¥ô·Nªº a, b $ \in$ R ¬Ò¦³

a . (- b) = (- a) . b = - (a . b).

µý ©ú. ­º¥ý¤À²M·¡ a . (- b) ¬O a ­¼¤W b ªº¥[ªk inverse, - a . b ¬O a ªº¥[ªk inverse ­¼¤W b ¦Ó - (a . b) ¬O a . b ªº¥[ªk inverse. ©Ò¥H­nÃÒ©ú a . (- b) = - (a . b) §Ú­Ì¥u­nÃÒ©ú (a . (- b)) + (a . b) = 0. µM¦Ó§Q¥Î (R8) ©M Lemma 5.2.1 ª¾

(a . (- b)) + (a . b) = a . ((- b) + b) = a . 0 = 0,

¬G±oÃÒ. ¦P²z¥i±o (- a) . b = - (a . b). $ \qedsymbol$

¦b¤@¯ëªº ring, R ¤¤ - a ¤£¤@©w¥i¥H¼g¦¨ (- 1) . a. ¥D­nªº­ì¦]¬O 1 ¤£¤@©w¦b R ¤¤, ©Ò¥H -1 ¤£¤@©w¦b R ¤¤. ¦]¦¹¦³¥i¯à¦b R ¤¤ (- 1) . a ¬O¨S¦³·N¸qªº. ¤£¹L¦pªG R ¬O¤@­Ó ring with 1, «h§Q¥Î Lemma 5.2.3 §Ú­Ì½T¹ê¥i±o

(- 1) . a = 1 . (- a) = - a    ¥B    a . (- 1) = - (a . 1) = - a.

§Q¥Î Lemma 5.2.3 §Ú­Ì¥i¥H±o¨ì¥H¤U¤j®a¼ô±xªºµ¥¦¡.

Corollary 5.2.4   ­Y R ¬O¤@­Ó ring ¥B a, b $ \in$ R «h

(- a) . (- b) = a . b.

µý ©ú. ¥ý§â - b ¬Ý¦¨¬O¤@¤¸¯À, ¬G§Q¥Î Lemma 5.2.3 ¥i±o (- a) . (- b) = - (a . (- b)). µM¦Ó¦b®M¥Î¤@¦¸ Lemma 5.2.3 ±o a . (- b) = - (a . b). µ²¦X¥H¤W¤Gµ¥¦¡±o

(- a) . (- b) = - (- (a . b)).

³Ì«á§Q¥Î Lemma 5.1.2 (1) ª¾ - (- (a . b)) = a . b, ¬G±oÃÒ (- a) . (- b) = a . b. $ \qedsymbol$

¥Ñ Lemma 5.2.3 ©M Corollary 5.2.4 §Ú­Ìª¾¹D ¡u-¡v ªº¹Bºâ©M§Ú­Ì¤@¯ë¼ô±xªº¹Bºâ¬Û¦P, ¥H«á§Ú­Ì±N¨Ì²ßºD±N a + (- b) ¼g¦¨ a - b.

¤j®aªì¦¸¬Ý¨ì ring ªº©w¸q®É©Î³|ºÃ´b¥[ªkªºµ²ºc¤¤¬°¦ó­n¨D¬O¤@­Ó abelian group? ¨Æ¹ê¤W¦pªG·íªì¶È­n¨D¥[ªk¬O¤@­Ó group ¦ý­¼ªk¦³ identity 1, «h³o·|`±j­¢' R ¦b¥[ªk¤§¤U¬O¤@­Ó abelian group. ³o¬O¦]¬°¹ï¥ô·Nªº a, b $ \in$ R, ¦Ò¼ (a + b) . (1 + 1) §Ú­Ì·|¦³¥H¤U¨â­Óµ¥¦¡:

(a + b) . (1 + 1) = a . (1 + 1) + b . (1 + 1) = (a + a) + (b + b),

(a + b) . (1 + 1) = (a + b) . 1 + (a + b) . 1 = (a + b) + (a + b).

¤]´N¬O»¡ a + a + b + b = a + b + a + b, ¬G¥i±o a + b = b + a.

³Ì«á§Ú­Ì­nª`·Nªº¬O: ·í n ¬O¤@­Ó¥¿¾ã¼Æ®É, ¬°¤F¤è«K¤@¯ë§Ú­Ì·|²ßºD¥Î na ¨Óªí¥Ü n ­Ó a ¬Û¥[©Ò±o¤§­È. ¨Ò¦p 2a = a + a, 3a = a + a + a, ...µ¥. ¤£¹L¤d¸U¤£­n§â 2a ¼g¦¨ 2 . a, na ¼g¦¨ n . a. ³o¬O¦]¬° 2 ©Î¬O¨ä¥Lªº n ¤£¤@©w·|¦b R ¤¤, ©Ò¥H n ©M a ¬O¤£¯à¬Û­¼ªº. ¨º»ò¹ï¥ô·Nªº¥¿¾ã¼Æ n ©M m, §Ú­Ì¤@¯ë¼ô±xªº (na) . (mb) = (nm)(a . b) ·|¹ï¶Ü? ³o¬O¨S¦³°ÝÃDªº, §A±N na ¼g¦¨ n ­Ó a ¬Û¥[, mb ¼g¦¨ m ­Ó b ¬Û¥[, ¦A§Q¥Î¤À°t²v (R8) ¦ÛµM¥iªº nm ­Ó a . b ¬Û¥[.


next up previous
¤U¤@­¶: Zero Divisor ©M Unit ¤W¤@­¶: ªì¯Å Ring ªº©Ê½è «e¤@­¶: Ring ªº°ò¥»©w¸q
Administrator 2005-06-18