Is the collection of irrational numbers R\ Qa field? Why or why not?

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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**Is the collection of irrational numbers \(\mathbb{R} \setminus \mathbb{Q}\) a field? Why or why not?**

In order for a set to be considered a field, it must satisfy several properties under two operations: addition and multiplication. It must be closed under these operations, have an additive identity (0) and a multiplicative identity (1), have additive inverses for every element, and every nonzero element must have a multiplicative inverse.

The collection of irrational numbers \(\mathbb{R} \setminus \mathbb{Q}\) does not form a field because it fails to satisfy the closure property under addition and multiplication. For example, the sum or product of two irrational numbers can be rational:

- \( \sqrt{2} \cdot \sqrt{2} = 2 \), which is a rational number.
- A specific example where an addition results in a rational number is \( (\sqrt{2} - \frac{\sqrt{2}}{2}) + \frac{\sqrt{2}}{2} = \sqrt{2} \), which should remain irrational, but does not showcase closure directly without specific examples resulting in rationals naturally.

Hence, \(\mathbb{R} \setminus \mathbb{Q}\) does not satisfy the field properties, primarily due to lack of closure under these operations.
Transcribed Image Text:**Is the collection of irrational numbers \(\mathbb{R} \setminus \mathbb{Q}\) a field? Why or why not?** In order for a set to be considered a field, it must satisfy several properties under two operations: addition and multiplication. It must be closed under these operations, have an additive identity (0) and a multiplicative identity (1), have additive inverses for every element, and every nonzero element must have a multiplicative inverse. The collection of irrational numbers \(\mathbb{R} \setminus \mathbb{Q}\) does not form a field because it fails to satisfy the closure property under addition and multiplication. For example, the sum or product of two irrational numbers can be rational: - \( \sqrt{2} \cdot \sqrt{2} = 2 \), which is a rational number. - A specific example where an addition results in a rational number is \( (\sqrt{2} - \frac{\sqrt{2}}{2}) + \frac{\sqrt{2}}{2} = \sqrt{2} \), which should remain irrational, but does not showcase closure directly without specific examples resulting in rationals naturally. Hence, \(\mathbb{R} \setminus \mathbb{Q}\) does not satisfy the field properties, primarily due to lack of closure under these operations.
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