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¤U¤@­¶: Quotient Field of an ¤W¤@­¶: ¤@¨Ç±`¨£ªº Rings «e¤@­¶: Ring of Polynomials over

Polynomials over the Integers

«e¤@³¹¸`ªºµ²ªG·íµM³£¥i¥H®M¥Î¨ì¦³²z«Y¼Æªº polynomials, ¦ý«o¤£¯à§¹§¹¾ã¾ãªº®M¥Î¨ì¾ã«Y¼Æªº polynomials. ³o¤@³¹§Ú­Ì±N¬Ý¬Ý¾ã«Y¼Æ©M¦³²z«Y¼Æ polynomials ªº²§¦P. ³Ì«á¦A§Q¥Î«e­±³¹¸`´£¨ì¾ã¼Æªº°ß¤@¤À¸Ñ©Ê¥H¤Î¦³²z«Y¼Æªº polynomial ring ªº°ß¤@¤À¸Ñ©Ê, ±o¨ì¾ã«Y¼Æªº polynomial ring ªº°ß¤@¤À¸Ñ©Ê.

§Ú­Ì¥O $ \mathbb {Q}$[x] ªí¥Ü©Ò¦³¦³²z«Y¼Æ polynomials ©Ò¦¨ªº¶°¦X¥B¥O $ \mathbb {Z}$[x] ªí¥Ü©Ò¦³¾ã«Y¼Æ polynomials ©Ò¦¨ªº¶°¦X. «e­±¤wª¾ $ \mathbb {Q}$[x] ¥Î¤@¯ëªº¥[ªk©M­¼ªk¥i§Î¦¨¤@­Ó ring, §Ú­ÌºÙ¤§¬° polynomial ring over $ \mathbb {Q}$. ¦P²z§Ú­Ì¤]¥i¥HÃÒ¥X $ \mathbb {Z}$[x] ¤]¬O¤@­Ó ring, §Ú­ÌºÙ¤§¬° polynomial ring over $ \mathbb {Z}$.

$ \mathbb {Z}$[x] ªº 0 ©M 1 ©M $ \mathbb {Q}$[x] ªº 0 ©M 1 ¬Û¦P. §Ú­Ì¤]¥i¦b $ \mathbb {Z}$[x] ¤¤©w¸q degree (¤Ï¥¿¥i¥H§â $ \mathbb {Z}$[x] ¬Ý¦¨ $ \mathbb {Q}$[x] ªº¤l¶°¦X). ©Ò¥H§Q¥Î©M Lemma 7.2.3 ¬Û¦PªºÃÒ©ú, §Ú­Ì¥i±o $ \mathbb {Z}$[x] ¬O¤@­Ó integral domain. $ \mathbb {Z}$[x] ©M $ \mathbb {Q}$[x] ³Ì¤jªº¤£¦P¬O $ \mathbb {Q}$[x] ¤¤©Ò¦³«D 0 ªº±`¼Æ³£¬O unit, µM¦Ó $ \mathbb {Z}$[x] ¤¤¥u¦³ ±1 ³o¨â­Ó±`¼Æ¬°¨ä unit. ³o¬O¦]¬°§Q¥Î Lemma 7.2.3 ªºÃÒ©ú§Ú­Ìª¾¹D $ \mathbb {Z}$[x] ¤¤ªº unit ¨ä degree ¤@©w¬O 0, ©Ò¥H¥u¦³±`¼Æ¤ ¥i¯à¬O $ \mathbb {Z}$[x] ªº unit, µM¦Ó¦]§Ú­Ì¥u¦Ò¼¾ã«Y¼Æ, ©Ò¥H¦b $ \mathbb {Z}$ ¤¤ªº unit ¤ ¥i¥H¬O $ \mathbb {Z}$[x] ªº unit, ¤]´N¬O ±1. ¦]¦¹³o¸Ì§Ú­Ì¥²¶·´£¿ô¤j®a, ¦b $ \mathbb {Z}$[x] ¤¤½Í¤À¸Ñ®É­n±N±`¼Æªº¤À¸Ñ¦C¤J¦Ò¼.

¦b Remark 7.2.5 ¤¤§Ú­Ì´£¤Î $ \mathbb {Z}$[x] ¤¤¨Ã¨S¦³¾l¦¡©w²z, ©Ò¥H¦b $ \mathbb {Q}$[x] ¤¤¥i§Q¥Î¾l¦¡©w²z±o¨ìªº©Ò¦³ ideal ³£¬O principle ideal (Theorem 7.2.6) ¹ï $ \mathbb {Z}$[x] ´N¤£¤@©w¹ï. ¨Æ¹ê¤W§Ú­Ì¥i¥H¦b $ \mathbb {Z}$[x] ¤¤§ä¨ì¤@­Ó (·íµM¤£¥u¤@­Ó) ideal ¥¦¤£¬O principle ideal.

Example 7.3.1   §Ú­Ì­n»¡©ú¦b $ \mathbb {Z}$[x] ¤¤ I = (2) + (x) ¤£¬O principle ideal. °²³] I ¬O principle ideal, §Y¦s¦b f (x) $ \in$ $ \mathbb {Z}$[x] ¨Ï±o I = $ \bigl($f (x)$ \bigr)$. §Q¥Î 2 $ \in$ I, §Ú­Ì±o¨ì 2 $ \in$ $ \bigl($f (x)$ \bigr)$, ¤]´N¬O¦s¦b h(x) $ \in$ $ \mathbb {Z}$[x] º¡¨¬ 2 = h(x) . f (x). §Q¥Î degree °¨¤W¥iª¾ deg(f (x)) = 0, ¤]´N¬O»¡ f (x) ¬O¤@­Ó±`¼Æ c $ \in$ $ \mathbb {Z}$. ²¦b§Q¥Î x $ \in$ I = $ \bigl($c$ \bigr)$ ª¾¦s¦b g(x) $ \in$ $ \mathbb {Z}$[x] ¨Ï±o x = c . g(x). ª`·N c . g(x) ³o¤@­Ó¦h¶µ¦¡¥¦ªº«Y¼Æ¤@©w¬O c ªº­¿¼Æ (§O§Ñ¤F g(x) $ \in$ $ \mathbb {Z}$[x], ©Ò¥H g(x) ªº«Y¼Æ³£¬O¾ã¼Æ). ¦]¦¹¥Ñ x = c . g(x) ª¾ x ³o¤@­Ó¦h¶µ¦¡ªº«Y¼ÆÀ³¸Ó¬O c ªº­¿¼Æ. µM¦Ó x ³o¤@­Ó¦h¶µ¦¡¥u¦³ x ³o¤@¶µ¥B¨ä«Y¼Æ¬O 1, ¬G±o c | 1, ¤]´N¬O c = ±1. ¦] c ¬O unit, Lemma 6.2.4 §i¶D§Ú­Ì I = $ \bigl($c$ \bigr)$ = $ \mathbb {Z}$[x], ´«¥y¸Ü»¡ 1 $ \in$ I = $ \bigl($2$ \bigr)$ + $ \bigl($x$ \bigr)$. §Q¥Î $ \bigl($2$ \bigr)$ + $ \bigl($x$ \bigr)$ ªº©w¸qª¾³oªí¥Ü¦s¦b n(x), m(x) $ \in$ $ \mathbb {Z}$[x] ¨Ï±o 1 = 2 . n(x) + x . m(x). ¤£¹L x . m(x) ¨S¦³±`¼Æ¶µ, ¦Ó 2 . n(x) ªº±`¼Æ¶µ¤@©w¬O 2 ªº­¿¼Æ, ©Ò¥H 2 . n(x) + x . m(x) ªº±`¼Æ¶µ¤@©w¤£¥i¯à¬° 1. ¬G·í n(x), m(x) $ \in$ $ \mathbb {Z}$[x] ®É 1 = 2 . n(x) + x . m(x) ¤£¥i¯à¦¨¥ß. ¦¹¥Ù¬Þµo¥Í©ó§Ú­Ìªº°²³] I ¬O principle ideal, ¬G±o I = $ \bigl($2$ \bigr)$ + $ \bigl($x$ \bigr)$ ¤£¥i¯à¬O $ \mathbb {Z}$[x] ªº principle ideal.

¦n¤F¬JµM $ \mathbb {Z}$[x] ¤¤ªº ideal ¤£¤@©w¬O principle ideal ¨º»ò§Ú­Ì´N¤£¯à¾Ç Proposition 7.2.11 ªº¤èªk±o¨ì $ \mathbb {Z}$[x] ¤¤ªº irreducible element ´N¬O prime element ¤F. ¤£¯à¥Î³o®M¤èªk¨Ã¤£ªí¥Üµ²ªG·|¿ù, ¦]¬°¦³¥i¯à¥Î¥t¤@®M¤èªk¥i¥H±o¨ì·Q­nªºµ²ªG°Ú! ¨S¿ù§Ú­Ì±N·|ÃÒ©ú¦b $ \mathbb {Z}$[x] ¤¤ªº irreducible element ©M prime element ¬O¬Û¦Pªº, ¤£¹L§Ú­Ì­nµo®i¥t¤@®Mªº¤èªk¨Ó±o¨ì.

³o­Ó¤èªk¨ä¹ê´N¬O­n§JªA«e­±´£¨ì $ \mathbb {Z}$[x] ©M $ \mathbb {Q}$[x] ³Ì¤jªº¤£¦P´N¬O¦b $ \mathbb {Z}$[x] ¤¤­n¦Ò¼±`¼Æªº¤À¸Ñ. µ¹©w f (x) = a0 + a1x + ... + anxn $ \in$ $ \mathbb {Z}$[x] ­n±N f (x) ¤À¸Ñ¦¨ degree ¤ñ¸û¤pªº polynomials ¬Û­¼¤§«e, ¥i¥H¥ý¦Ò¼¥i¤£¥i¥H´£¥X¤@­Ó±`¼Æ¥X¨Ó (¦]¬°­Y³o­Ó±`¼Æ¤£¬O ±1 ¨º»ò¦b $ \mathbb {Z}$[x] ¤¤³o´Nºâ¬O¤@­Ó``¦³®Ä''ªº¤À¸Ñ). ¥i¥H´£¥X¬Æ»ò±`¼Æ¥X¨Ó©O? ¤j®a³£·|·Q¨ì´£¥X¨º¨Ç«Y¼Æ a0, a1,..., an ªº³Ì¤j¤½¦]¼Æ§a! ©Ò¥H§Ú­Ì¦³¥H¤U²³æ¦ý­«­n¤§µ²ªG.

Lemma 7.3.2   ­Y f (x) $ \in$ $ \mathbb {Z}$[x] ¬O¤@­Ó«D 0 ªº polynomial, «h f (x) ¥i°ß¤@¼g¦¨ f (x) = c . f*(x), ¨ä¤¤ c $ \in$ $ \mathbb {N}$, f*(x) $ \in$ $ \mathbb {Z}$[x] ¥B f*(x) ªº«Y¼Æªº³Ì¤j¤½¦]¼Æ¬O 1.

µý ©ú. ­º¥ýÃÒ©ú¦s¦b©Ê: ­Y f (x) = a0 + a1x + ... + anxn, ¥O d = gcd(a0, a1,..., an). ¥Ñ³Ì¤j¤½¦]¼Æªº©Ê½èª¾ a0 = d . b0, a1 = d . b1,..., an = d . bn ¥B gcd(b0, b1,..., bn) = 1. ¬G¥i±N f (x) ¼g¦¨ d . (b0 + b1x + ... + bnxn) ¬°©Ò­n¨Dªº§Î¦¡.

±µµÛÃÒ©ú°ß¤@©Ê: °²³] f (x) = c . f*(x), ¨ä¤¤ c $ \in$ $ \mathbb {N}$ ¥B f*(x) $ \in$ $ \mathbb {Z}$[x]. ±N c ­¼¤J f*(x) ªº¦U¶µ«Y¼Æ¤¤, ª¾ f (x) ªº©Ò¦³«Y¼Æ a0, a1,..., an ³£·|¬O c ªº­¿¼Æ. ¤]´N¬O c ¬O a0, a1,..., an ªº¤½¦]¼Æ. ¦pªG c$ \ne$d = gcd(a0, a1,..., an), «h f*(x) ªº«Y¼Æ¤¤·|¦³ d /c ³o¤@­Ó¤£¬O 1 ªº¤½¦]¼Æ, ¦¹©M f*(x) ªº¦U¶µ«Y¼Æªº³Ì¤j¤½¦]¼Æ¬° 1 ¬Û¥Ù¬Þ. ¬G±o d = c, ¤]´N¬O»¡ d . f*(x) = d . (b0 + b1x + ... + bnxn). ³Ì«á¦] $ \mathbb {Z}$[x] ¬O integral domain, §Ú­Ì±o f*(x) = b0 + b1x + ... + bnxn. $ \qedsymbol$

¦³¤F Lemma 7.3.2, §Ú­Ì¦³¥H¤Uªº©w¸q.

Definition 7.3.3   ­Y f (x) $ \in$ $ \mathbb {Z}$[x] ¥i¼g¦¨ f (x) = c . f*(x), ¨ä¤¤ c $ \in$ $ \mathbb {N}$, f*(x) $ \in$ $ \mathbb {Z}$[x] ¥B f*(x) ªº«Y¼Æªº³Ì¤j¤½¦]¼Æ¬O 1. «hºÙ c ¬° f (x) ªº content, °O¬° c(f ). ­Y f (x) $ \in$ $ \mathbb {Z}$[x] ¥B c(f )= 1, «hºÙ f (x) ¬O¤@­Ó primitive polynomial.

¨ä¹ê c(f ) ´N¬O f (x) ªº©Ò¦³«Y¼Æªº³Ì¤j¤½¦]¼Æ. Lemma 7.3.2 §i¶D§Ú­Ì»¡¥ô·Nªº f (x) $ \in$ $ \mathbb {Z}$[x] ³£¥i¥H¼g¦¨¨ä content ­¼¤W¤@­Ó primitive polynomial. §Ú­Ì¥i¥H±N Lemma 7.3.2 ±À¼s¨ì $ \mathbb {Q}$[x] ¤¤.

Proposition 7.3.4   ­Y f (x) $ \in$ $ \mathbb {Q}$[x] ¬O¤@­Ó«D 0 ªº polynomial, «h f (x) ¥i°ß¤@¼g¦¨ f (x) = c . f*(x), ¨ä¤¤ c $ \in$ $ \mathbb {Q}$, c > 0 ¥B f*(x) $ \in$ $ \mathbb {Z}$[x] ¬O¤@­Ó primitive polynomial.

µý ©ú. ­º¥ýÃÒ©ú¦s¦b©Ê: ­Y f (x) = a0 + a1x + ... + anxn, ¨ä¤¤ ai $ \in$ $ \mathbb {Q}$. §Ú­Ì¥i§ä¨ì¤@¥¿¾ã¼Æ m ¨Ï±o m . f (x) $ \in$ $ \mathbb {Z}$[x] (¤ñ¤è»¡¥O m ¬° ³o¨Ç ai ¤À¥Àªº­¼¿n). ¬JµM m . f (x) $ \in$ $ \mathbb {Z}$[x] ¥Ñ Lemma 7.3.2 ªº¦s¦b©Êª¾¦s¦b¥¿¾ã¼Æ a ¥H¤Î f*(x) $ \in$ $ \mathbb {Z}$[x] ¨ä¤¤ f*(x) ¬O primitive polynomial, ¨Ï±o m . f (x) = a . f*(x). ¬G±o

f (x) = $\displaystyle {\frac{a}{m}}$ . f*(x)

¬°©Ò­n¨Dªº§Î¦¡.

¦Ü©ó°ß¤@©Ê§Ú­Ì°²³] f (x) = d . f*(x) = d' . g(x) ¨ä¤¤ d, d' ³£¬O¥¿ªº¦³²z¼Æ¦Ó f*(x), g(x) $ \in$ $ \mathbb {Z}$[x] ³£¬O primitive polynomials. ±N d ©M d' ¤À§O¼g¦¨ a/b ©M a'/b', ¨ä¤¤ a, a', b, b' $ \in$ $ \mathbb {N}$. §Ú­Ì¥i±o

(a . b') . f*(x) = (a' . b) . g(x).

§O§Ñ¤F (a . b') . f*(x),(a' . b) . g(x) $ \in$ $ \mathbb {Z}$[x] ¤S¦] a . b', a' . b $ \in$ $ \mathbb {N}$ ¥B f*(x), g(x) ³£¬O primitive polynomial, ¥Ñ Lemma 7.3.2 ªº°ß¤@©Êª¾: a . b' = b . a' (§Y d = d') ¥B f*(x) = g(x). ¬G±oÃҰߤ@©Ê. $ \qedsymbol$

¥Ñ Proposition 7.3.4, §Ú­Ì¥i¥H§â content ªº©w¸q±À¼s¨ì $ \mathbb {Q}$[x], ¥H«á§Ú­Ì±N·|§â¥ô·Nªº f (x) $ \in$ $ \mathbb {Q}$[x] ¼g¦¨ f (x) = c(f ) . f*(x), ¨ä¤¤ 0 < c(f ) $ \in$ $ \mathbb {Q}$ ¬O f (x) ªº content, f*(x) $ \in$ $ \mathbb {Z}$[x] ¬O¤@­Ó primitive polynomial.

·í f (x), g(x) $ \in$ $ \mathbb {Q}$[x], ­n­pºâ f (x) . g(x) ªº content, ¨ä¹ê¬O«Ü½ÆÂøªº. §Ú­Ì¥²¶·§â¨â­Ó polynomial ­¼¶, ²¾¶µ¾ã²z, ¦A³q¤À§ä³Ì¤j¤½¦]¼Æ. §Ú­Ì·íµM§Æ±æ f (x) . g(x) ªº content ¥i¥H¥Ñ f (x) ©M g(x) ªº contents ª½±µ¨D¥X´N¦n¤F. Åý§Ú­Ì¥ý¬Ý¤@­Ó¯S®í¨Ò¤l´N¬O f (x) ©M g(x) ªº contents ³£¬O 1 ªº±¡ªp.

Lemma 7.3.5 (Gauss Lemma)   ­Y f (x), g(x) $ \in$ $ \mathbb {Z}$[x] ³£¬O primitive polynomials, «h f (x) . g(x) ¤]¬O¤@­Ó primitive polynomial.

µý ©ú. ³] f (x) = anxn + ... + a1x + a0, g(x) = bmxm + ... + b1x + b0, §Ú­Ì­n¥Î¤ÏÃÒªkÃÒ©ú­Y c(f )= c(g) = 1, «h c(f . g) = 1. °²³] c(f . g) = d$ \ne$1, ¨ú¤@½è¼Æ p ¨Ï±o p | d, ¤]´N¬O p ¾ã°£ f (x) . g(x) ªº©Ò¦³«Y¼Æ. µM¦] c(f )= c(g) = 1, ¬G¥²¦s¦b ai, bj ¨Ï±o p$ \nmid$ai ¥B p$ \nmid$bj. ¥O r ¬O³Ì¤pªº¾ã¼Æ¨Ï±o p$ \nmid$ar (¤]´N¬O p$ \nmid$ar, ¦ý¹ï¥ô·Nªº i < r, p | ai), ¦P¼Ëªº¥O s ¬O³Ì¤pªº¾ã¼Æ¨Ï±o p$ \nmid$bs. ²Æ[¹î f (x) . g(x) ªº xr + s ¶µ«Y¼Æ:

$\displaystyle \sum_{i+j=r+s}^{}$ai . bj.

°£¤F ar . bs ¥H¥ , ¨ä¥L¶µªº ai . bj ­n¤£¬O i < r ´N¬O j < s. §_«h­Y i > r ¥B j > s ¨º»ò i + j > r + s ´N¤£¥i¯à²Å¦X i + j = r + s ¤F. ¦pªG i < r ¥Ñ·íªì r ªº¿ï¨úª¾ p | ai, ¬Gª¾¦¹±¡ªp¤U p | ai . bj. ¦P²z, ­Y j < s ¤]¥i±o p | ai . bj. Á`¦Ó¨¥¤§, f (x) . g(x) ªº xr + s ¶µªº«Y¼Æ°£¤F ar . bs ¥ ¨ä¥Lªº ai . bj ³£¥i³Q p ¾ã°£. µM¦Ó·íªì°²³] p$ \nmid$ar ¥B p$ \nmid$bs, ¬Gª¾ p$ \nmid$ar . bs. ¤]´N¬O»¡ f (x) . g(x) ªº xr + s ¶µªº«Y¼Æ¤£¥i³Q p ¾ã°£. ³o©M·íªì°²³] p ¥i¾ã°£ f (x) . g(x) ªº¨C¤@¶µªº«Y¼Æ¬Û¥Ù¬Þ. ¬Gª¾¤£¥i¯à c(f . g)$ \ne$1, ©Ò¥H f (x) . g(x) ¤]¬O primitive polynomial. $ \qedsymbol$

¦³¤F Gauss Lemma ¹ï©ó¤@¯ëªº f (x), g(x) $ \in$ $ \mathbb {Q}$[x], §Ú­Ì«Ü§Öªº´N¥i¥H­pºâ¥X c(f . g).

Proposition 7.3.6   ­Y f (x), g(x) $ \in$ $ \mathbb {Q}$[x] ³£¬O«D 0 ªº polynomial, «h

c(f . g) = c(f ) . c(g).

µý ©ú. ¥Ñ Lemma 7.3.4 ª¾¥i±N f (x) ©M g(x) ¤À§O¼g¦¨ f (x) = c(f ) . f*(x) ©M g(x) = c(g) . g*(x), ¨ä¤¤ f*(x) ©M g*(x) ³£¬O primitive polynomials. ¬G±o

f (x) . g(x) = $\displaystyle \bigl($c(f ) . c(g)$\displaystyle \bigr)$ . $\displaystyle \bigl($f*(x) . g*(x)$\displaystyle \bigr)$.

¦A¥Ñ Lemma 7.3.4 ª¾ f (x) . g(x) ¥i°ß¤@¼g¦¨ c(f . g) . h(x) ¨ä¤¤ h(x) ¬O primitive polynomial. µM¦Ó Lemma 7.3.5 §i¶D§Ú­Ì f*(x) . g*(x) ¬O primitive polynomial, ¬G¥Ñ°ß¤@©Êª¾ f*(x) . g*(x) = h(x) ¥B c(f ) . c(g) = c(f . g). $ \qedsymbol$

±µ¤U¨Ó§Ú­Ì­n½Í $ \mathbb {Z}$[x] ¤Wªº¤À¸Ñ, ­º¥ý­n°Ï¤À¤@¤U¦b $ \mathbb {Z}$[x] ©M $ \mathbb {Q}$[x] ¤¤ªº¾ã°£·§©À. µ¹©w f (x), g(x) $ \in$ $ \mathbb {Z}$[x], §Ú­Ì»¡ f (x) | g(x) in $ \mathbb {Z}$[x] ªí¥Ü¦s¦b h(x) $ \in$ $ \mathbb {Z}$[x] º¡¨¬ g(x) = h(x) . f (x). ¦Ó§Ú­Ì»¡ f (x) | g(x) in $ \mathbb {Q}$[x] ªí¥Ü¦s¦b l (x) $ \in$ $ \mathbb {Q}$[x] º¡¨¬ g(x) = l (x) . f (x). ³o¸Ì³Ì¤jªº¤£¦P¦b©ó h(x) ­n¨D¸¨¦b $ \mathbb {Z}$[x], ¦Ó l (x) ­n¦b $ \mathbb {Q}$[x] §Y¥i. ©Ò¥H¦³¥i¯àµo¥Í f (x) | g(x) in $ \mathbb {Q}$[x] ¦ý f (x)$ \nmid$g(x) in $ \mathbb {Z}$[x] ªºª¬ªp.

Lemma 7.3.7   °²³] f (x), g(x) $ \in$ $ \mathbb {Z}$[x], ¥B f (x) ¬O¤@­Ó primitive polynomial, «h f (x) | g(x) in $ \mathbb {Z}$[x] ­Y¥B°ß­Y f (x) | g(x) in $ \mathbb {Q}$[x].

µý ©ú. °²³] f (x) | g(x) in $ \mathbb {Z}$[x] ªí¥Ü¦s¦b h(x) $ \in$ $ \mathbb {Z}$[x] º¡¨¬ g(x) = h(x) . f (x). µM¦Ó h(x) $ \in$ $ \mathbb {Z}$[x] ·íµM±o h(x) $ \in$ $ \mathbb {Q}$[x], ¬Gª¾ f (x) | g(x) in $ \mathbb {Q}$[x]. (ª`·N³o³¡¤À§Ú­Ì¤£»Ý­n f (x) ¬O primitive ªº°²³].)

¤Ï¤§, ­Y f (x) | g(x) in $ \mathbb {Q}$[x], ªí¥Ü¦s¦b l (x) $ \in$ $ \mathbb {Q}$[x] º¡¨¬ g(x) = l (x) . f (x). §Ú­Ì§Æ±æ¯àÃÒ±o l (x) $ \in$ $ \mathbb {Z}$[x]. §Q¥Î Lemma 7.3.4 ±N l (x) ¼g¦¨ l (x) = c(l ) . l*(x), ¨ä¤¤ l*(x) ¬O primitive polynomials. ¬G±o g(x) = c(l ) . (l*(x) . f (x)). ¦]¬° f (x) ©M l*(x) ³£¬O primitive polynomials, ¬G§Q¥Î Lemma 7.3.5 ª¾ l*(x) . f (x) ¬O primitive polynomial. ¦A§Q¥Î Lemma 7.3.4 ªº°ß¤@©Êª¾ c(g) = c(l ). ¦] c(g) $ \in$ $ \mathbb {N}$, ¬G±o c(l ) $ \in$ $ \mathbb {N}$, ¥B¤S l*(x) $ \in$ $ \mathbb {Z}$[x], ¬G¥Ñ l (x) = c(l ) . l*(x) ±o l (x) $ \in$ $ \mathbb {Z}$[x]. $ \qedsymbol$

¦P¼Ëªº, §Ú­Ì¤]­n°Ï¤À¤@¤U¦b $ \mathbb {Q}$[x] ©M $ \mathbb {Z}$[x] ¤¤¤À¸Ñªº¤£¦P. ­Y f (x) $ \in$ $ \mathbb {Z}$[x] §Ú­Ì»¡ f (x) ¦b $ \mathbb {Q}$[x] ¥i¤À¸Ñªí¥Ü f (x) ¥i¼g¦¨ f (x) = g(x) . h(x), ¨ä¤¤ g(x), h(x) $ \in$ $ \mathbb {Q}$[x] ¥B deg(g(x)) ©M deg(h(x)) ¬Ò¤p©ó deg(f (x)). ¦ý³o¨Ã¤£ªí¥Ü f (x) ¥i¥H¦b $ \mathbb {Z}$[x] ¤¤¤À¸Ñ¦¨ f (x) = m(x) . n(x), ¨ä¤¤ m(x), n(x) $ \in$ $ \mathbb {Z}$[x]. ¤£¹L¤U¤@­Ó Lemma §i¶D§Ú­Ì³o¬O¿ì±o¨ìªº.

Lemma 7.3.8   °²³] f (x) $ \in$ $ \mathbb {Z}$[x] ¥B f (x) = g(x) . h(x) ¨ä¤¤ g(x), h(x) $ \in$ $ \mathbb {Q}$[x], «h¦s¦b m(x), n(x) $ \in$ $ \mathbb {Z}$[x] º¡¨¬ f (x) = m(x) . n(x) ¥B deg(m(x)) = deg(g(x)) ¤Î deg(n(x)) = deg(h(x)).

µý ©ú. §Q¥Î Lemma 7.3.4 ª¾ g(x) = c(g) . g*(x) ¥B h(x) = c(h) . h*(x) ¨ä¤¤ g*(x), h*(x) $ \in$ $ \mathbb {Z}$[x] ¥B³£¬O primitive polynomial. §Q¥Î Proposition 7.3.6 ª¾

c(g) . c(h) = c(g . h) = c(f ),

µM¦Ó f (x) $ \in$ $ \mathbb {Z}$[x], ¬G c(g) . c(h) = c(f ) $ \in$ $ \mathbb {N}$. ¦]¦¹­Y¥O m(x) = $ \bigl($c(g) . c(h)$ \bigr)$ . g*(x) $ \in$ $ \mathbb {Z}$[x] ¤Î n(x) = h*(x) $ \in$ $ \mathbb {Z}$[x], «h
f (x) = g(x) . h(x) = $\displaystyle \bigl($c(g) . g*(x)$\displaystyle \bigr)$ . $\displaystyle \bigl($c(h) . h*(x)$\displaystyle \bigr)$  
  = $\displaystyle \bigl($c(g) . c(h)$\displaystyle \bigr)$ . g*(x) . h*(x)  
  = m(x) . n(x).  

¤S

deg(m(x)) = deg(g*(x)) = deg(g(x))    ¥B    deg(n(x)) = deg(h*(x)) = deg(h(x)).

$ \qedsymbol$

¤Ï¤§­Y f (x) ¦b $ \mathbb {Z}$[x] ¥i¥H¤À¸Ñ¦¨ f (x) = m(x) . n(x), ¨ä¤¤ m(x), n(x) $ \in$ $ \mathbb {Z}$[x], ¥B m(x), n(x) ¤£¬O $ \mathbb {Z}$[x] ¤¤ªº unit. ¨º»ò ¤j®a¤@©w»¬°¥Ñ©ó m(x), n(x) ¤]¦b $ \mathbb {Q}$[x] ¤¤©Ò¥H f (x) ¦b $ \mathbb {Q}$[x] ¤¤¥i¥H¤À¸Ñ. ¨ä¹ê¤£µM, ¦]¬° m(x), n(x) ¦b $ \mathbb {Z}$[x] ¤¤¤£¬O unit, ¦ý¥i¯à¦b $ \mathbb {Q}$[x] ¤¤´N¬O unit ¤F. ¨Ò¦p 2x + 2 ¦b $ \mathbb {Q}$[x] ¬O irreducible ¦ý¦b $ \mathbb {Z}$[x] ¤¤ 2x + 2 = 2 . (x + 1), ¦Ó¥B 2 ©M x + 1 ¦b $ \mathbb {Z}$[x] ¤¤³£¤£¬O unit (¦ý 2 ¦b $ \mathbb {Q}$[x] ¬O unit), ©Ò¥H 2x + 2 ¦b $ \mathbb {Z}$[x] ¨Ã¤£¬O irreducible. ±q³o¸Ì¬Ý¥X $ \mathbb {Z}$[x] ¤¤ªº irreducible element ©M $ \mathbb {Q}$[x] ªº irreducible element ¤£¦P.

¦^ÅU¤@¤U§Ú­Ì©w¸q©Ò¿×ªº irreducible element ¬O¤@­Ó¤¸¯À¥¦ªº divisor ¥u¦³ unit ©M ¥»¨­­¼¤W unit ³o¨âºØ§Î¦¡. ¥Ñ©ó $ \mathbb {Z}$[x] ¤¤ªº unit ¥u¦³ 1 ©M -1 ©Ò¥H§Ú­Ì¦³¥H¤Uªº©w¸q.

Definition 7.3.9   ¥O p(x) $ \in$ $ \mathbb {Z}$[x]
  1. ­Y p(x) ¦b $ \mathbb {Z}$[x] ¤¤ªº divisor ¥u¦³ ±1 ©M ±p(x), «hºÙ p(x) ¬O $ \mathbb {Z}$[x] ªº irreducible element.
  2. ­Y¹ï©Ò¦³º¡¨¬ p(x) | f (x) . g(x) ªº f (x), g(x) $ \in$ $ \mathbb {Z}$[x] ³£¦³ p(x) | f (x) ©Î p(x) | g(x) «hºÙ p(x) ¬O $ \mathbb {Z}$[x] ªº prime element.

¥Ñ³o­Ó©w¸q§Ú­Ì°¨¤W±o¨ì¥H¤Uªº Lemma.

Lemma 7.3.10   °²³] p(x) $ \in$ $ \mathbb {Z}$[x] ¥B deg(p(x)) > 0.
  1. ­Y p(x) ¬O¤@­Ó irreducible element, «h p(x) ¬O¤@­Ó primitive polynomial.
  2. ­Y p(x) ¬O¤@­Ó prime element, «h p(x) ¬O¤@­Ó primitive polynomial.

µý ©ú. (1) °²³] p(x) ¬O irreducible. ¦] p(x) = c(p) . p*(x), ¨ä¤¤ c(p) $ \in$ $ \mathbb {N}$ $ \subseteq$ $ \mathbb {Z}$[x] ¥B p*(x) $ \in$ $ \mathbb {Z}$[x], ©Ò¥H c(p) ¬O p(x) ªº¤@­Ó divisor. ¥Ñ p(x) ¬O irreducible ¤Î deg(p*(x)) = deg(p(x)) > 0 ª¾ c(p) = 1, ¬G±o p(x) ¬O primitive.

(2) °²³] p(x) ¬O prime. ¦] p(x) = c(p) . p*(x), ¬Gª¾ p(x) | c(p) . p*(x). ¥Ñ p(x) ¬O prime ªº°²³], ª¾ p(x) | c(p) ©Î p(x) | p*(x). ¥Ñ©ó deg(p(x)) > 0 ª¾¤£¥i¯à p(x) | c(p). ¬G±o p(x) | p*(x). ¤]´N¬O»¡¦s¦b $ \lambda$(x) $ \in$ $ \mathbb {Z}$[x] ¨Ï±o p*(x) = $ \lambda$(x) . p(x). ¬G±o p*(x) = $ \bigl($$ \lambda$(x) . c(p)$ \bigr)$ . p*(x). §Q¥Î $ \mathbb {Z}$[x] ¬O integral domain ¤Î p*(x)$ \ne$ 0 ª¾ $ \lambda$(x) . c(p) = 1. ¤]´N¬O»¡ $ \lambda$(x) ©M c(p) ¬O $ \mathbb {Z}$[x] ªº unit. ¦ý¥Ñ©w¸q c(p) ¬O¥¿¾ã¼Æ, ¬G±o $ \lambda$(x) = c(p) = 1. ¤]´N¬O»¡ p(x) ¬O primitive. $ \qedsymbol$

¦p«e­±´X¸`¤¤ªºµ²ªG, §Ú­Ì±N·|ÃÒ±o¦b $ \mathbb {Z}$[x] ¤¤ªº irreducible element ©M prime element ¬O¤@¼Ëªº. ¥Ñ©ó $ \mathbb {Z}$[x] ¨S¦³©Ò¦³ªº ideal ³£¬O principle ideal ªº©Ê½è, §Ú­Ì¤£¯à¥Î«e­±ªº¤èªk¦pªkªw»s. §Ú­Ì±N§Q¥Î $ \mathbb {Q}$[x] ¤¤ªº irreducible element ªº©Ê½è¨ÓÀ°¦£³B²z, ©Ò¥H§Ú­Ì»Ý­n¥ý¤F¸Ñ¦b $ \mathbb {Z}$[x] ¤¤ªº irreducible element ©M $ \mathbb {Q}$[x] ¤¤ªº irreducible element ¤§¶¡ªºÃö«Y.

Lemma 7.3.11   ­Y p(x) $ \in$ $ \mathbb {Z}$[x], deg(p(x)) > 0 ¥B p(x) ¬O¤@­Ó primitive polynomial, «h p(x) ¬O $ \mathbb {Q}$[x] ¤¤ªº irreducible element ­Y¥B°ß­Y p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element.

µý ©ú. ­º¥ý°²³] p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element. ¦pªG p(x) ¦b $ \mathbb {Q}$[x] ¤¤¤£¬O irreducible element, ªí¥Ü¦s¦b g(x), h(x) $ \in$ $ \mathbb {Q}$[x] º¡¨¬ 0 < deg(g(x)) < deg(p(x)), 0 < deg(h(x)) < deg(p(x)) ¥B p(x) = g(x) . h(x). §Q¥Î Lemma 7.3.8 ª¾¦s¦b m(x), n(x) $ \in$ $ \mathbb {Z}$[x] ¥B deg(m(x)) = deg(g(x)), deg(n(x)) = deg(h(x)) º¡¨¬ p(x) = m(x) . n(x). ¤]´N¬O»¡ m(x) ¬O p(x) ªº divisor. ¦ý 0 < deg(m(x)) < deg(p(x)), ¬Gª¾ m(x)$ \ne$±1 ¥B m(x)$ \ne$±p(x). ¦¹©M p(x) ¬O $ \mathbb {Z}$[x] ªº¤@­Ó irreducible element °²³]¬Û¥Ù¬Þ. ¬Gª¾ p(x) ¤]¬O $ \mathbb {Q}$[x] ¤¤ªº irreducible element.

¤Ï¤§, ­Y p(x) ¬O $ \mathbb {Q}$[x] ¤¤ªº irreducible element. ­Y p(x) = m(x) . n(x), ¨ä¤¤ m(x), n(x) $ \in$ $ \mathbb {Z}$[x]. ¥Ñ p(x) ¦b $ \mathbb {Q}$[x] ¬O irreducible ªº°²³]ª¾ m(x) ©M n(x) ¤¤¦³¤@­Ó¬O $ \mathbb {Q}$[x] ªº unit, §Y±`¼Æ: ´N°²³] m(x) = d ¬O±`¼Æ§a! ¦] m(x) $ \in$ $ \mathbb {Z}$[x] ¬Gª¾ d $ \in$ $ \mathbb {Z}$. ¥Ñ p(x) = d . n(x) ª¾ d ¬O p(x) ªº©Ò¦³«Y¼Æªº¤½¦]¼Æ. ¦ý¤wª¾ p(x) ¬O primitive, ¬G±o d = ±1. ¤]´N¬O»¡ p(x) ªº divisor ¥u¯à¬O ±1 ©M ±p(x) ³oºØ§Î¦¡, ¬G±o p(x) ¦b $ \mathbb {Z}$[x] ¤¤¬O irreducible. $ \qedsymbol$

¥Ñ©ó $ \mathbb {Q}$ ¬O¤@­Ó field, ©Ò¥H¤W¤@¸`¤¤ F[x] ªº©Ê½è³£¥i®M¥Î¦b $ \mathbb {Q}$[x] ¤W. §Ú­Ì­n§Q¥Î $ \mathbb {Q}$[x] ¤¤ªº irreducible ©M prime ¬O¤@¼Ëªº, ±o¨ì¦b $ \mathbb {Z}$[x] ¤¤ªº irreducible ©M prime ¤]¬O¤@¼Ëªº.

Proposition 7.3.12   °²³] p(x) $ \in$ $ \mathbb {Z}$[x]. ­Y p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element, «h p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº prime element. ¤Ï¤§, ­Y p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº prime element, «h p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element.

µý ©ú. ­º¥ýª`·N, ·í deg(p(x)) = 0 ®Éªí¥Ü p(x) $ \in$ $ \mathbb {Z}$ ¬O¤@­Ó±`¼Æ. §Ú­Ì¤wª¾¦b $ \mathbb {Z}$ ¤¤ªº irreducible ©M prime ¬O¤@¼Ëªº (Proposition 7.1.7), ©Ò¥H§Ú­Ì¥u­nÃö¤ß deg(p(x)) > 0 ªº±¡ªp.

­º¥ý°²³] p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element. ¥Ñ Lemma 7.3.10 ª¾¨ä¬° primitive, ¬G¥Ñ Lemma 7.3.11 ª¾ p(x) ¤]¬O $ \mathbb {Q}$[x] ¤¤ªº irreducible element. ¦A¥Ñ Proposition 7.2.11 ª¾ p(x) ¬O $ \mathbb {Q}$[x] ¤¤ªº prime element. ²­Y f (x), g(x) $ \in$ $ \mathbb {Z}$[x] ¥B p(x) | f (x) . g(x) in $ \mathbb {Z}$[x], ¥Ñ Lemma 7.3.7 ª¾ p(x) | f (x) . g(x) in $ \mathbb {Q}$[x]. ¬G¥Ñ p(x) ¦b $ \mathbb {Q}$[x] ¬O prime ±o p(x) | f (x) ©Î p(x) | g(x) in $ \mathbb {Q}$[x]. ¦A¥Ñ Lemma 7.3.7 ª¾ p(x) | f (x) ©Î p(x) | g(x) in $ \mathbb {Z}$[x]. ¤]´N¬O»¡ p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº prime element.

¤Ï¤§, ­Y p(x) ¬O $ \mathbb {Z}$[x] ¤¤ªº prime element. ­Y p(x) = m(x) . n(x) ¨ä¤¤ m(x), n(x) $ \in$ $ \mathbb {Z}$[x]. «h¥Ñ©ó p(x) | m(x) . n(x), ¥i±o p(x) | n(x) ©Î p(x) | m(x). ­Y p(x) | n(x), §Y¦s¦b $ \lambda$(x) $ \in$ $ \mathbb {Z}$[x] ¨Ï±o n(x) = $ \lambda$(x) . p(x). ¬G±o

n(x) = $\displaystyle \lambda$(x) . $\displaystyle \bigl($n(x) . m(x)$\displaystyle \bigr)$ = $\displaystyle \bigl($$\displaystyle \lambda$(x) . m(x)$\displaystyle \bigr)$ . n(x).

¥Ñ n(x)$ \ne$ 0 ¥H¤Î $ \mathbb {Z}$[x] ¬O integral domain, ±o $ \lambda$(x) . m(x) = 1. ¤]´N¬O»¡ m(x) ¬O $ \mathbb {Z}$[x] ªº unit, §Y m(x) = ±1. ¦P²z, ­Y p(x) | m(x) ¥i±o n(x) = ±1. ±oÃÒ p(x) ªº divisor ³£¬O ±1 ©M ±p(x) ³oºØ§Î¦¡, ¬Gª¾ p(x) ¬O¤@­Ó irreducible element. $ \qedsymbol$

²¦b­nÃÒ©ú $ \mathbb {Z}$[x] ¤Wªº°ß¤@¤À¸Ñ©Ê½èÅS¥X¤F¤@½uÀÆ¥ú, «e­±´X¸`¤¤§Ú­ÌÃÒ©ú°ß¤@¤À¸Ñ©Ê½è¨Ã¨S¦³¥Î¨ì¨C¤@­Ó ideal ³£¬O principle ideal ªº©Ê½è, ¦Ó¬O¥Î¨ì¦p Proposition 7.3.12 ¤¤¨C­Ó irreducible element ¬O prime ªº©Ê½è. ¦p¦P¦b¾ã¼Æªº±¡ªp, ¥Ñ©ó f (x) ©M - f (x) ªº¤À¸Ñ¶È®t¤@­Ó¥¿­t¸¹, §Ú­Ì¥i¥H¥u¦Ò¼³Ì°ª¦¸¶µ«Y¼Æ¬O¥¿¾ã¼Æªº polynomial.

Theorem 7.3.13   ­Y f (x) $ \in$ $ \mathbb {Z}$[x] ¬O¤@­Ó¤£¬° 0, 1, - 1 ¥B³Ì°ª¦¸¶µ«Y¼Æ¬O¥¿¾ã¼Æªº polynomial, «h¦s¦b p1(x),..., pr(x) $ \in$ $ \mathbb {Z}$[x], ¨ä¤¤³o¨Ç pi(x) ¬O $ \mathbb {Z}$[x] ¤¤¨â¨â¬Û²§¥B³Ì°ª¦¸¶µ«Y¼Æ¬O¥¿¾ã¼Æªº irreducible elements, º¡¨¬

f (x) = p1(x)n1 ... pr(x)nr,    ni $\displaystyle \in$ $\displaystyle \mathbb {N}$,$\displaystyle \forall$i $\displaystyle \in$ {1,..., r}.

¦pªG f (x) ¥i¥H¤À¸Ñ¦¨¥t¥ ªº§Î¦¡ f (x) = q1(x)m1 ... qs(x)ms, ¨ä¤¤³o¨Ç qi(x) ¤]¬O $ \mathbb {Z}$[x] ¤¤¨â¨â¬Û²§¥B³Ì°ª¦¸«Y¼Æ¬O¥¿¾ã¼Æªº irreducible elements, «h r = s ¥B¸g¹LÅÜ´«¶¶§Ç¥i±o pi(x) = qi(x), ni = mi, $ \forall$ i $ \in$ {1,..., r}.

µý ©ú. ­º¥ýÃÒ©ú¦s¦b©Ê, ¤]´N¬O f (x) ¥i¼g¦¨¦³­­¦h­Ó $ \mathbb {Z}$[x] ¤¤ªº irreducible elements ªº­¼¿n. §Ú­Ì¨ÌµM (¹ï degree) ¥Î¼Æ¾ÇÂk¯Çªk¨ÓÃÒ©ú. °²³] deg(f (x)) = 0, ¦] f (x) $ \in$ $ \mathbb {N}$ ¥B¤£¬O unit, ¬G¥Ñ $ \mathbb {Z}$ ªº¤À¸Ñ©Ê½è (Theorem 7.1.8) ªº¦s¦b©Êª¾ f (x) ¥i¼g¦¨¦³­­¦h­Ó irreducible elements ªº­¼¿n. ²°²³]¦s¦b©Ê¹ï degree ¤p©ó n ªº polynomial ¬Ò¦¨¥ß. ·í deg(f (x)) = n ®É, ­Y f (x) ¥»¨­¬O irreducible, ¦s¦b©Ê¦ÛµM¦¨¥ß. ¬G¶È³Ñ f (x) ¤£¬O irreducible ªº±¡ªp­n¦Ò¼. ¦¹®É­nª`·N, ¦b $ \mathbb {Z}$[x] ¤¤¤@­Ó polynomial ¬O irreducible ¨Ã¤£ªí¥Ü¥L¤@©w¥i¥H¼g¦¨¨â­Ó degree ¤ñ¸û¤pªº polynomials ªº­¼¿n (¨Ò¦p«e­±´£¹Lªº¨Ò¤l 2x + 2). ¦¹®É§Ú­Ì¥ý±N f (x) ¼g¦¨ f (x) = c(f ) . f*(x), ¨ä¤¤ f*(x) $ \in$ $ \mathbb {Z}$[x] ¬O primitive polynomial. ¥Ñ©ó c(f ) $ \in$ $ \mathbb {N}$, ¦A¤@¦¸§Q¥Î Theorem 7.1.8 ª¾ c(f )= 1 ©Î¬O¥i¥H¼g¦¨¦³­­¦h­Ó irreducible ±`¼Æ polynomials ªº­¼¿n. ©Ò¥H§Ú­Ì¥u³Ñ¤U¦Ò¼ f*(x) ¬O§_¥i¼g¦¨¦³­­¦h­Ó irreducible elements ªº­¼¿n. ·í f*(x) ¬O irreducible ®É, ¦s¦b©Ê¦ÛµM¤S¦¨¥ß¤F. ¦Ó·í f*(x) ¤£¬O irreducible ®É, Lemma 7.3.11 §i¶D§Ú­Ì f*(x) ¦b $ \mathbb {Q}$[x] ¤£¬O irreducible, ¤]´N¬O f*(x) = g(x) . h(x) ¨ä¤¤ g(x), h(x) $ \in$ $ \mathbb {Q}$[x] ¥B 0 < deg(g(x)) < deg(f (x)) ¥H¤Î 0 < deg(h(x)) < deg(f (x)). ¥Ñ Lemma 7.3.8 ª¾¦s¦b m(x), n(x) $ \in$ $ \mathbb {Z}$[x] ¥B deg(m(x)) = deg(g(x)) ¥H¤Î deg(n(x)) = deg(h(x)) ¨Ï±o f*(x) = m(x) . n(x). ¥Ñ©ó deg(m(x)) < deg(f (x)) = n ¥H¤Î deg(n(x)) < n, ¬G§Q¥ÎÂk¯Çªk°²³]ª¾ m(x) ©M n(x) ³£¥i¼g¦¨¦³­­¦h­Ó irreducible elements ªº­¼¿n. ¦]¦¹±oÃÒ f*(x) ¥i¥H¼g¦¨¦³­­¦h­Ó irreducible elements ªº­¼¿n, ¬Gª¾ f (x) = c(f )f*(x) ¤]¥i¼g¦¨¦³­­¦h­Ó irreducible elements ªº­¼¿n.

¦Ü©ó°ß¤@©Ê§Ú­Ì¨ÌµM¥Î¼Æ¾ÇÂk¯Çªk¨Ó³B²z. ­Y deg(f (x)) = 0, ¦] f (x) $ \in$ $ \mathbb {N}$, ¬G¥i¥H§Q¥Î Theorem 7.1.8 ªº°ß¤@©Ê±oÃҰߤ@©Ê. ²°²³]°ß¤@©Ê¹ï degree ¤p©ó n ªº polynomial ¬Ò¦¨¥ß. ·í deg(f (x)) = n ®É, ­Y

f (x) = p1(x)n1 ... pr(x)nr = q1(x)m1 ... qs(x)ms,

¨ä¤¤ pi(x) ¨â¨â¬Û²§, qj(x) ¤]¬O¨â¨â¬Û²§, ¦Ó¥B pi(x), qj(x) ³£¬O $ \mathbb {Z}$[x] ¤¤³Ì°ª¦¸¶µ«Y¼Æ¬O¥¿¾ã¼Æªº irreducible elements. ¥Ñ©ó deg(f (x)) > 0, ¬Gª¾ pi(x) ¤¤¥²¦s¦b¤@ polynomial ¨ä degree ¤j©ó 0, ¸g­«±Æ«á§Ú­Ì¥O¤§¬° p1(x). Proposition 7.3.12 §i¶D§Ú­Ì p1(x) ¬O $ \mathbb {Z}$[x] ªº prime element, ¬G¥Ñ p1(x) | f (x) ±oª¾, qj(x) ¤¤¦³¤@ polynomial ·|³Q p1(x) ¾ã°£, ¸g­«±Æ«á§Ú­Ì¥O¤§¬° q1(x). ¤]´N¬O»¡ p1(x) | q1(x). µM¦Ó q1(x) ¬O irreducible, ¨ä divisor ¥u¦³ ±1 ©M ±q1(x). ¤S¦]¤wª¾ deg(p1(x)) > 0 ¥B p1(x) ©M q1(x) ªº³Ì°ª¦¸¶µ«Y¼Æ³£¬O¥¿¾ã¼Æ, ¬G±o p1(x) = q1(x). ¦]¦¹§Ú­Ì¥i±N f (x) ªº¤À¸Ñ§ï¼g¦¨

f (x) = p1(x)n1 . p2(x)n2 ... pr(x)nr = p1(x)m1 . q2(x)m2 ... qs(x)ms.

±N¤W¦¡²¾¶µ¦A´£¥X p1(x), §Ú­Ì¥i±o

p1(x) . $\displaystyle \bigl($p1(x)n1 - 1 . p2(x)n2 ... pr(x)nr - p1(x)m1 - 1 . q2(x)m2 ... qs(x)ms$\displaystyle \bigr)$ = 0.

¥Ñ©ó p1(x)$ \ne$ 0 ¥B $ \mathbb {Z}$[x] ¬O integral domain, §Ú­Ì±o

p1(x)n1 - 1 . p2(x)n2 ... pr(x)nr - p1(x)m1 - 1 . q2(x)m2 ... qs(x)ms = 0.

²¥O g(x) = p1(x)n1 - 1 . p2(x)n2 ... pr(x)nr. ¥Ñ©ó·íªì¿ï¨ú p1(x) º¡¨¬ deg(p1(x)) > 0, ¬G±o

deg(g(x)) = deg(f (x)) - deg(p1(x)) < deg(f (x)) = n

¥B

g(x) = p1(x)n1 - 1 . p2(x)n2 ... pr(x)nr = p1(x)m1 - 1 . q2(x)m2 ... qs(x)ms

¬O g(x) ªº¨â­Ó¤À¸Ñ, ¬G§Q¥ÎÂk¯Çªk°²³]§Ú­Ì¦³ r = s ¥B p1(x) = q1(x),..., pr(x) = qr(x) ¥H¤Î n1 = m1, n2 = m2,..., nr = mr, ¬G±oÃҰߤ@©Ê. $ \qedsymbol$

¥Ñ Theorem 7.3.13 ª¾ $ \mathbb {Z}$[x] ¤¤ªº irreducible elements ´N¦p¦P $ \mathbb {Z}$ ¤¤ªº½è¼Æ¤@¼Ë­«­n. ¥t¤@¤è­±§Q¥Î Lemma 7.3.8 ¤]§i¶D§Ú­Ì¦b $ \mathbb {Z}$[x] ¤¤ªº irreducible element ¦b $ \mathbb {Q}$[x] ¤¤¤]¬O irreducible. ¦]¦¹±´°Q $ \mathbb {Z}$[x] ¤¤¦³­þ¨Ç irreducible elements ¬O¤@­Ó­«­nªº½ÒÃD. ¨ä¹êµ¹©w f (x) $ \in$ $ \mathbb {Z}$[x] ­n§PÂ_¨ä¬O§_¬° irreducible ¨Ã¤£®e©ö. ¥H¤U§Ú­Ì¤¶²Ð¤@ºØ¤èªk¥i¥H½T»¬Y¤@Ãþªº polynomial ¬O irreducible.

Proposition 7.3.14 (Eisenstein Criterion)   ¥O

f (x) = xn + an - 1xn - 1 + ... + a1x + a0 $\displaystyle \in$ $\displaystyle \mathbb {Z}$[x],

¨ä¤¤ n > 0. °²³]¦s¦b¤@½è¼Æ p $ \in$ $ \mathbb {N}$ º¡¨¬

p | a0p | a1, ..., p | an - 1    ¦ý    p2$\displaystyle \nmid$a0,

«h f (x) ¬O $ \mathbb {Z}$[x] ¤¤ªº irreducible element.

µý ©ú. ¥Ñ©ó c(f )= 1 ©Ò¥H f (x) ¬O primitive polynomial. ¦]¦¹­n»¡©ú f (x) ¬O irreducible in $ \mathbb {Z}$[x] ¥u­n»¡©ú f (x) ¤£¥i¯à¼g¦¨¨â­Ó degree ¤p©ó n ªº polynomials ªº­¼¿n. §Ú­Ì§Q¥Î¤ÏÃÒªk¨ÓÃÒ©ú.

°²³] f (x) = g(x) . h(x) ¨ä¤¤

g(x) = crxr + ... + c1x + c0 $\displaystyle \in$ $\displaystyle \mathbb {Z}$[x],    0 < r < n

¥B

h(x) = dsxs + ... + d1x + d0 $\displaystyle \in$ $\displaystyle \mathbb {Z}$[x],    0 < s < n.

¦Ò¼ g(x) . h(x) ªº±`¼Æ¶µ c0 . d0 = a0. ¥Ñ°²³] p | a0 = c0 . d0, ¬Gª¾ p | c0 ©Î p | d0. µM¦Ó¤Sª¾ p2$ \nmid$c0 . d0, ¬Gª¾ c0 ©M d0 ¶¡¥u¯à¦³¤@­Ó³Q p ¾ã°£. §Ú­Ì´N°²³]¬O c0 §a! ¤]´N¬O»¡ p | c0 ¦ý p$ \nmid$d0. ²¦bÆ[¹î g(x) . h(x) ªº¤@¦¸¶µ«Y¼Æ c0 . d1 + c1 . d0 = a1. ¥Ñ°²³] p | a1 ¥H¤Î­è¤ ±oª¾ªº p | c0 ¥i±o p | c1 . d0. ¦ý¤Sª¾ p$ \nmid$d0 ¬G±o p | c1. ³o¼Ë¤@ª½¤U¥h§Ú­Ì·Q¥Î¼Æ¾ÇÂk¯ÇªkÃÒ±o p | cr. ¤]´N¬O°²³]¤wª¾ p | c0, p | c1,..., p | cr - 1, §Ú­Ì±ýÃÒ±o p | cr. ²¦Ò¼ g(x) . h(x) ªº xr ¶µ«Y¼Æ

c0 . dr + c1 . dr - 1 + ... + cr - 1 . d1 + cr . d0 = ar.

(³o­Ó¦¡¤l¸Ì­Y s < r, ¨º·íµM¬O¥O ds + 1 = ... = dr = 0) ¥Ñ©ó 0 < r < n ¬Gª¾ p | ar, ¦A¥[¤WÂk¯Ç°²³] p | c0,..., p | cr - 1, §Ú­Ì¥i±o p | cr . d0. §O§Ñ¤F p$ \nmid$d0, ¬G±oÃÒ p | cr. ²¦b§Ú­Ì¦Ò¼ g(x) . h(x) ªº³Ì°ª¦¸¶µ«Y¼Æ (§Y f (x) ªº xn ¶µ«Y¼Æ)

cr . ds = 1.

¤j®a°¨¤W¬Ý¥X¥Ñ p | cr ¤£¥i¯à±o¨ì cr . ds = 1. ¦]¦¹±o¨ì¥Ù¬Þ, ¤]´N¬O»¡ f (x) ¬O $ \mathbb {Z}$[x] ªº irreducible element. $ \qedsymbol$

³Ì«á§Ú­Ì­«¥Ó¤@¤U, ¥Ñ Lemma 7.3.8 (©Î Lemma 7.3.11) §Ú­Ìª¾¹D²Å¦X Proposition 7.3.14 ªº polynomials ¦b $ \mathbb {Q}$[x] ¤]¬O irreducible.


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¤U¤@­¶: Quotient Field of an ¤W¤@­¶: ¤@¨Ç±`¨£ªº Rings «e¤@­¶: Ring of Polynomials over
Administrator 2005-06-18