7. Show that the set Z of integers is NOT a vector space.

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Linear Algebra

**Problem 7: Vector Space Verification**

**Objective:** Demonstrate why the set \(\mathbb{Z}\) of integers is NOT a vector space.

To prove that \(\mathbb{Z}\) is not a vector space, we need to check whether it satisfies the axioms required for a vector space over a field, typically the field of real numbers \(\mathbb{R}\).

### Key Vector Space Axioms:
1. **Closure under addition:** For any two integers \(a, b \in \mathbb{Z}\), the sum \(a + b\) should also be in \(\mathbb{Z}\), which holds true.
2. **Existence of additive identity:** There exists an element \(0 \in \mathbb{Z}\) such that \(a + 0 = a\) for all \(a \in \mathbb{Z}\), which also holds true.
3. **Existence of additive inverses:** For each \(a \in \mathbb{Z}\), there exists an element \(-a \in \mathbb{Z}\) such that \(a + (-a) = 0\), which holds true.
4. **Closure under scalar multiplication:** For a scalar \(c \in \mathbb{R}\) and an integer \(a \in \mathbb{Z}\), the product \(c \cdot a\) must also be in \(\mathbb{Z}\). This axiom fails because, for example, if \(c = 0.5\) (a real number) and \(a = 2\), then \(c \cdot a = 1\), which is not an integer.
5. **Other axioms** regarding associativity, distributivity, etc., are irrelevant if closure under scalar multiplication fails.

### Conclusion:
Since the set of integers \(\mathbb{Z}\) fails to satisfy closure under scalar multiplication, it does not meet all the criteria to be a vector space. Thus, \(\mathbb{Z}\) is NOT a vector space.
Transcribed Image Text:**Problem 7: Vector Space Verification** **Objective:** Demonstrate why the set \(\mathbb{Z}\) of integers is NOT a vector space. To prove that \(\mathbb{Z}\) is not a vector space, we need to check whether it satisfies the axioms required for a vector space over a field, typically the field of real numbers \(\mathbb{R}\). ### Key Vector Space Axioms: 1. **Closure under addition:** For any two integers \(a, b \in \mathbb{Z}\), the sum \(a + b\) should also be in \(\mathbb{Z}\), which holds true. 2. **Existence of additive identity:** There exists an element \(0 \in \mathbb{Z}\) such that \(a + 0 = a\) for all \(a \in \mathbb{Z}\), which also holds true. 3. **Existence of additive inverses:** For each \(a \in \mathbb{Z}\), there exists an element \(-a \in \mathbb{Z}\) such that \(a + (-a) = 0\), which holds true. 4. **Closure under scalar multiplication:** For a scalar \(c \in \mathbb{R}\) and an integer \(a \in \mathbb{Z}\), the product \(c \cdot a\) must also be in \(\mathbb{Z}\). This axiom fails because, for example, if \(c = 0.5\) (a real number) and \(a = 2\), then \(c \cdot a = 1\), which is not an integer. 5. **Other axioms** regarding associativity, distributivity, etc., are irrelevant if closure under scalar multiplication fails. ### Conclusion: Since the set of integers \(\mathbb{Z}\) fails to satisfy closure under scalar multiplication, it does not meet all the criteria to be a vector space. Thus, \(\mathbb{Z}\) is NOT a vector space.
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