Chapter 14: Problem 14
Give an example of a ring with eight elements. How about one with 16 elements? Generalize.
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Chapter 14: Problem 14
Give an example of a ring with eight elements. How about one with 16 elements? Generalize.
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Determine whether or not each of the following sets of numbers is a ring under ordinary addition and multiplication. a) \(R=\) the set of positive integers and zero b) \(R=\\{k n \mid n \in \mathbf{Z}, k\) a fixed positive integer\\} c) \(R=\\{a+b \sqrt{2} \mid a, b \in \mathbf{Z}\\}\) d) \(R=\\{a+b \sqrt{2}+c \sqrt{3} \mid a \in \mathbf{Z}, b, c \in \mathbf{Q}\\}\)
Let \(R=\left\\{a+b i \mid a, b \in \mathbf{Z}, i^{2}=-1\right\\}\), with addition and multiplication defined by \((a+b i)+(c+d i)=(a+c)+\) \((b+d) i\) and \((a+b i)(c+d i)=(a c-b d)+(b c+a d) i\), respectively. (a) Verify that \(R\) is an integral domain. (b) Determine all units in \(R\).
Write a computer program (or develop an algorithm) that reverses the order of the digits in a given positive integer. For example, the input 1374 should result in the output 4731 .
Given \(n\) positive integers \(x_{1}, x_{2}, \ldots, x_{n}\), not necessarily
distinct, prove that either \(n \mid\left(x_{1}+x_{2}+\cdots+x_{t}\right)\), for
some \(1 \leq i \leq n\), or there exist \(1 \leq i
a) In how many ways can one select two positive integers \(m, n\), not necessarily distinct, so that \(1 \leq m \leq 100\), \(1 \leq n \leq 100\) and the last digit of \(7^{m}+3^{n}\) is \(8 ?\) b) Answer part (a) for the case where \(1 \leq m \leq 125,1 \leq\) \(n \leq 125 .\) c) If one randomly selects \(m, n\) [as in part (a)], what is the probability that 2 is now the last digit of \(7^{m}+3^{n}\) ?
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