Let A, B be set with A non-empty. (a) Prove that if A C B, then A, B are not disjoint. (b) What if we remove the assumption "A is non-empty"? Is the state- ment in (a) still correct? Prove or provide a counterexample.

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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For this homework, you can use the following facts. If it is a definition, you should mention "by definition" or "by definition of XXX (e.g. even)". If it is not a definition, you do NOT have to cite.

1. **Basic algebra**, such as \(2 + 2 = 4\), \(1 - 3 = -2\), \(2 \cdot 4 = 8\). This includes subtracting an integer, or dividing by a non-zero rational/real/complex number.

2. Common knowledge of whether numbers are integer/rational, e.g. \(\frac{1}{2}\) is not an integer, \(\pi\) is not rational, all integers are rational, all rational numbers are real, all real numbers are complex, etc.

3. **Associative law of addition**: \((a + b) + c = a + (b + c)\), and **associative law of multiplication**: \((ab)c = a(bc)\), for all \(a, b, c \in \mathbb{C}\).

4. **Commutative law of addition**: \(a + b = b + a\), and **commutative law of multiplication**: \(ab = ba\), for all \(a, b \in \mathbb{C}\).

5. **Distributive Law**: For all \(a, b, c \in \mathbb{C}\), we have \((a + b)(c + d) = ac + ad + bc + bd\). In particular, \((a + b)^2 = a^2 + 2ab + b^2\).

6. An integer \(n\) is **even** if there exists an integer \(k\) such that \(n = 2k\).

7. An integer \(n\) is **odd** if there exists an integer \(k\) such that \(n = 2k + 1\).

8. All integers are either even or odd.

9. A real number \(x\) is **positive** if \(x > 0\), and **negative** if \(x < 0\).

10. All real numbers are either positive, negative, or 0.

11. Let \(A, B\) be subsets of a universal set \(U\).
    -
Transcribed Image Text:For this homework, you can use the following facts. If it is a definition, you should mention "by definition" or "by definition of XXX (e.g. even)". If it is not a definition, you do NOT have to cite. 1. **Basic algebra**, such as \(2 + 2 = 4\), \(1 - 3 = -2\), \(2 \cdot 4 = 8\). This includes subtracting an integer, or dividing by a non-zero rational/real/complex number. 2. Common knowledge of whether numbers are integer/rational, e.g. \(\frac{1}{2}\) is not an integer, \(\pi\) is not rational, all integers are rational, all rational numbers are real, all real numbers are complex, etc. 3. **Associative law of addition**: \((a + b) + c = a + (b + c)\), and **associative law of multiplication**: \((ab)c = a(bc)\), for all \(a, b, c \in \mathbb{C}\). 4. **Commutative law of addition**: \(a + b = b + a\), and **commutative law of multiplication**: \(ab = ba\), for all \(a, b \in \mathbb{C}\). 5. **Distributive Law**: For all \(a, b, c \in \mathbb{C}\), we have \((a + b)(c + d) = ac + ad + bc + bd\). In particular, \((a + b)^2 = a^2 + 2ab + b^2\). 6. An integer \(n\) is **even** if there exists an integer \(k\) such that \(n = 2k\). 7. An integer \(n\) is **odd** if there exists an integer \(k\) such that \(n = 2k + 1\). 8. All integers are either even or odd. 9. A real number \(x\) is **positive** if \(x > 0\), and **negative** if \(x < 0\). 10. All real numbers are either positive, negative, or 0. 11. Let \(A, B\) be subsets of a universal set \(U\). -
Let \( A, B \) be set with \( A \) non-empty.

(a) Prove that if \( A \subseteq B \), then \( A, B \) are not disjoint.

(b) What if we remove the assumption "A is non-empty"? Is the statement in (a) still correct? Prove or provide a counterexample.
Transcribed Image Text:Let \( A, B \) be set with \( A \) non-empty. (a) Prove that if \( A \subseteq B \), then \( A, B \) are not disjoint. (b) What if we remove the assumption "A is non-empty"? Is the statement in (a) still correct? Prove or provide a counterexample.
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