17. Let R be an integral domain. Assume that the Division Algorithm always holds in R[x). Prove that Ris a field. 18. Let e:R- R be the function that maps each polynomial in Rx] onto its constant term (an element of R). Show that e is a surjective homomorphism of rings 19. Let eZx] -ZJx] be the function that maps the polynomial a + ax +...+

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ISBN:9780470458365
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b MATLAB: An Introduction with A X
Thomas W. Hungerford - Abstrac ×
+
O File | C:/Users/angel/Downloads/Thomas%20W.%20Hungerford%20-%20Abstract%20Algebra_%20AN%20lntroduction-Cengage%20Learning%20(2014).pdf
-- A' Read aloud V Draw
F Highlight
O Erase
117
of 621
(b) Give an example in Z[x] to show that part (a) may be false if the leading
coefficient of g(x) is not a unit. [Hint: Exercise 5(b) with Z in place of Q.]
Ceursu
15. Let R be a commutative ring with identity and a e R.
(a) If a = Or, show that 12 + ax is a unit in R[x]. [Hint: Consider 1 - ax +
a*x*]
(b) If a' = Og, show that 1g + ax is a unit in R[x].
16. Let R be a commutative ring with identity and a e R. If 12 + ax is a unit in
R[x], show that d = Og for some integer n> 0. [Hint: Suppose that the inverse
of 1g + ax is bo + bjx + bx + ...+ b. Since their product is 1g, bo = 1r
(Why?) and the other coefficients are all Og.]
17. Let R be an integral domain. Assume that the Division Algorithm always
holds in R[x]. Prove that R is a field.
18. Let o:R[x] → R be the function that maps each polynomial in R[x] onto its
constant term (an element of R). Show that o is a surjective homomorphism
of rings.
19. Let ç:Z[x] →Z,[x] be the function that maps the polynomial a, + ajx + . ..+
ax in Z[x] onto the polynomial [ao] + [q]x + • . . + [a]x*, where [a] denotes
the class of the integer a in Z,. Show that o is a surjective homomorphism of
rings.
20. Let D:R[x]→ R[x] be the derivative map defined by
D(a + ax + ax++ax) = a¡ + 2azx + 3azx +...+ na,-.
Is Da homomorphism of rings? An isomorphism?
C.21. Let h:R- S be a homomorphism of rings and define a function h:R[x] -> S[x]
by the rule
h(ao + ajx + ...+ ax) = h(a) + h(aj)x + h(a)x² +...+ h(a,)xª.
Prove that Snt
(a) h is a homomorphism of rings.
(b) k is injective if and only if h is injective.
(c) h is surjective if and only if h is surjective.
(d) If R = S, then R[x] = S[x].
22. Let R be a commutative ring and let k(x) be a fixed polynomial in R[x). Prove
that there exists a unique homomorphism o:R[x] → R[x] such that
P(r) = r for allre R
and
p(x) = k(x).
4.2
Divisibility in F[x]
All the results of Section 1.2 on divisibility and greatest common divisors in Z now
carry over, with only minor modifications, to the ring of polynomials over a field.
11:12 AM
e Type here to search
EPIC
Ai
EPIC
99+
10/30/2020
Transcribed Image Text:b MATLAB: An Introduction with A X Thomas W. Hungerford - Abstrac × + O File | C:/Users/angel/Downloads/Thomas%20W.%20Hungerford%20-%20Abstract%20Algebra_%20AN%20lntroduction-Cengage%20Learning%20(2014).pdf -- A' Read aloud V Draw F Highlight O Erase 117 of 621 (b) Give an example in Z[x] to show that part (a) may be false if the leading coefficient of g(x) is not a unit. [Hint: Exercise 5(b) with Z in place of Q.] Ceursu 15. Let R be a commutative ring with identity and a e R. (a) If a = Or, show that 12 + ax is a unit in R[x]. [Hint: Consider 1 - ax + a*x*] (b) If a' = Og, show that 1g + ax is a unit in R[x]. 16. Let R be a commutative ring with identity and a e R. If 12 + ax is a unit in R[x], show that d = Og for some integer n> 0. [Hint: Suppose that the inverse of 1g + ax is bo + bjx + bx + ...+ b. Since their product is 1g, bo = 1r (Why?) and the other coefficients are all Og.] 17. Let R be an integral domain. Assume that the Division Algorithm always holds in R[x]. Prove that R is a field. 18. Let o:R[x] → R be the function that maps each polynomial in R[x] onto its constant term (an element of R). Show that o is a surjective homomorphism of rings. 19. Let ç:Z[x] →Z,[x] be the function that maps the polynomial a, + ajx + . ..+ ax in Z[x] onto the polynomial [ao] + [q]x + • . . + [a]x*, where [a] denotes the class of the integer a in Z,. Show that o is a surjective homomorphism of rings. 20. Let D:R[x]→ R[x] be the derivative map defined by D(a + ax + ax++ax) = a¡ + 2azx + 3azx +...+ na,-. Is Da homomorphism of rings? An isomorphism? C.21. Let h:R- S be a homomorphism of rings and define a function h:R[x] -> S[x] by the rule h(ao + ajx + ...+ ax) = h(a) + h(aj)x + h(a)x² +...+ h(a,)xª. Prove that Snt (a) h is a homomorphism of rings. (b) k is injective if and only if h is injective. (c) h is surjective if and only if h is surjective. (d) If R = S, then R[x] = S[x]. 22. Let R be a commutative ring and let k(x) be a fixed polynomial in R[x). Prove that there exists a unique homomorphism o:R[x] → R[x] such that P(r) = r for allre R and p(x) = k(x). 4.2 Divisibility in F[x] All the results of Section 1.2 on divisibility and greatest common divisors in Z now carry over, with only minor modifications, to the ring of polynomials over a field. 11:12 AM e Type here to search EPIC Ai EPIC 99+ 10/30/2020
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