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College Algebra Exam Review 300

# College Algebra Exam Review 300 - 6.6.7 Show that R D Z C x...

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310 6. RINGS root r=s , where r and s are relatively prime, then s divides a n and r divides a 0 . In particular, if the polynomial is monic, then its only rational roots are integers. 6.6.4. Generalize the previous exercise to polynomials over a unique fac- torization domain. 6.6.5. Complete the details of this alternative proof of Gauss’s Lemma: Let R be a UFD. For any irreducible p 2 R , consider the quotient map p W R ! R=pR , and extend this to a homomorphism p W ROExŁ ! .R=pR/OExŁ , defined by p . P a i x i / D P i p .a i /x i , using Corollary 6.2.8 . (a) Show that a polynomial h.x/ is in the kernel of p if, and only if, p is a common divisor of the coefficients of h.x/ . (b) Show that f .x/ 2 ROExŁ is primitive if, and only if, for all irre- ducible p , p .f .x// ¤ 0 . (c) Show that .R=pR/OExŁ is integral domain for all irreducible p . (d) Conclude that if f .x/ and g.x/ are primitive in ROExŁ , then f .x/g.x/ is primitive as well. 6.6.6. Show that Z OE p satisfies the ascending chain condition for prin- cipal ideals but has irreducible elements that are not prime.
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Unformatted text preview: 6.6.7. Show that R D Z C x Q ŒxŁ does not satisfy the ascending chain condition for principal ideals. Show that irreducibles in R are prime. 6.7. Noetherian Rings This section can be skipped without loss of continuity. The rings Z ŒxŁ and KŒx;y;zŁ are not principal ideal domains. How-ever, we shall prove that they have the weaker property that every ideal is ﬁnitely generated—that is, for every ideal I there is a ﬁnite set S such that I is the ideal generated by S . A condition equivalent to the ﬁnite generation property is the ascend-ing chain condition for ideals . Deﬁnition 6.7.1. A ring (not necessarily commutative, not necessarily with identity) satisﬁes the ascending chain condition (ACC) for ideals if every strictly increasing sequence of ideals has ﬁnite length. We denote the ideal generated by a subset S of a ring R by .S/ ....
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