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Give the characteristic for each of the following rings: a) \(\mathbf{Z}_{11}\) b) Z.s. \([x]\) c) \(Q[x]\) d) \(\mathbf{Z}[\sqrt{5}]=\\{a+b \sqrt{5} \mid a, b \in \mathbf{Z}\\}\), under the ordinary operations of addition and multiplication of real numbers

Short Answer

Expert verified
The characteristics for the given rings are: a) \(\mathbf{Z}_{11}\) is 11; b) Z.s. \([x]\) is 0; c) \(Q[x]\) is 0; d) \(\mathbf{Z}[\sqrt{5}]\) is 0.

Step by step solution

01

Determine the characteristic of \(\mathbf{Z}_{11}\)

The ring \(\mathbf{Z}_{11}\) represents the set of integers modulo 11. Here, the characteristic is 11 because 11•1 mod 11 is 0.
02

Determine the characteristic of Z.s. \([x]\)

The ring of integer polynomials is denoted by Z.s. \([x]\). Here, the characteristic is 0 because the only way to get zero through sum of units (which is 1) is to sum zero times.
03

Determine the characteristic of \(Q[x]\)

The ring \(Q[x]\) represents the set of all polynomials with rational coefficients. Here, the characteristic is also 0, for the same reason as in Step 2.
04

Determine the characteristic of \(\mathbf{Z}[\sqrt{5}]\)

Finally, the ring \(\mathbf{Z}[\sqrt{5}]\) represents the set of all real numbers of the form \(a+b \sqrt{5}\) where \(a\) and \(b\) are integers. Since the integers are a subset, the characteristic is 0, same as for the ring of integers.

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