(2) Let R = Z[√5] and R* = R−0. Consider the nomm map N : R* → Z*. If a, b = Z, we set N(a+b√-5) = (a+b√−5)(a − b√−5) = a² + 5b². Show that if x, y = R*, then N(xy) = N(x)N(y). (b) Show that u € R* is a unit if and only N(u) is a unit in Z. (c) Let U(R) be the set of units in R. Show that U(R) = {−1, +1}.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Let R = Z[√5] and R* = R-0. Consider the nomm map N : R* → Z*.
If a, b = Z, we set N(a+b√-5) = (a +b√-5)(a − b√-5) = a² +5b².
Show that if x, y = R*, then N(xy) = N(x)N(y).
(b) Show that u € R* is a unit if and only N(u) is a unit in Z.
(c) Let U(R) be the set of units in R. Show that U(R) = {−1, +1}.
Transcribed Image Text:(2) Let R = Z[√5] and R* = R-0. Consider the nomm map N : R* → Z*. If a, b = Z, we set N(a+b√-5) = (a +b√-5)(a − b√-5) = a² +5b². Show that if x, y = R*, then N(xy) = N(x)N(y). (b) Show that u € R* is a unit if and only N(u) is a unit in Z. (c) Let U(R) be the set of units in R. Show that U(R) = {−1, +1}.
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