(4) Determine ker ø. (5) Prove that the quotient ring Z[√-1] In is a field if and only if q = n² + 1 is prime.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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How do you do question 4 and 5?

The following assignment will use repeatedly the following ring
Z[√ 1] = {r + √-1s : r, s € Z},
the Gaussian integers. This is a subset of C and it is a commutative ring. (You don't need to prove these properties -
you can assume them.)
-
Throughout this question let 0 ‡ n € Z and let In = z[√=1]{√−1− n). Set q = n² + 1 and denote the equivalence
class of r € Z mod q by [r].
(1) Prove that Z[√-1] is an integral domain.
(2) Find the order of Z[√-1]×, the group of units of Z[√-1], and determine whether or not it is cyclic.
(3) Show that the map (for all r, s € Z)
: Z[√1] → Z/qZ, (r+√√-1s) = [r] + [n][s].
is a surjective ring homomorphism.
(4) Determine ker ø.
(5) Prove that the quotient ring
Z[√-1
In
is a field if and only if q = n² + 1 is prime.
Transcribed Image Text:The following assignment will use repeatedly the following ring Z[√ 1] = {r + √-1s : r, s € Z}, the Gaussian integers. This is a subset of C and it is a commutative ring. (You don't need to prove these properties - you can assume them.) - Throughout this question let 0 ‡ n € Z and let In = z[√=1]{√−1− n). Set q = n² + 1 and denote the equivalence class of r € Z mod q by [r]. (1) Prove that Z[√-1] is an integral domain. (2) Find the order of Z[√-1]×, the group of units of Z[√-1], and determine whether or not it is cyclic. (3) Show that the map (for all r, s € Z) : Z[√1] → Z/qZ, (r+√√-1s) = [r] + [n][s]. is a surjective ring homomorphism. (4) Determine ker ø. (5) Prove that the quotient ring Z[√-1 In is a field if and only if q = n² + 1 is prime.
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