Measure Theory

Description: This quiz covers the fundamental concepts and theorems of Measure Theory, a branch of mathematics that deals with the measurement of sets and functions.
Number of Questions: 14
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Which of the following is not a property of a measure (\mu) on a set (X): (\mu(\emptyset) = 0), (\mu(A \cup B) = \mu(A) + \mu(B)) for disjoint sets (A) and (B), or (\mu(A) \leq \mu(B)) whenever (A \subseteq B)?

  1. (\mu(\emptyset) = 0)

  2. (\mu(A \cup B) = \mu(A) + \mu(B)) for disjoint sets (A) and (B)

  3. (\mu(A) \leq \mu(B)) whenever (A \subseteq B)


Correct Option: B
Explanation:

The correct answer is (\mu(A \cup B) = \mu(A) + \mu(B)) for disjoint sets (A) and (B). This is known as the additivity property of a measure.

Let (\mu) be a measure on a set (X). If (A_1, A_2, \ldots) is a sequence of sets in (X) such that (A_n \subseteq A_{n+1}) for all (n), then what is the limit of (\mu(A_n)) as (n) approaches infinity?

  1. (\mu(\cup_{n=1}^\infty A_n))

  2. (\mu(\cap_{n=1}^\infty A_n))

  3. (\lim_{n\to\infty} \mu(A_n))


Correct Option: A
Explanation:

The correct answer is (\mu(\cup_{n=1}^\infty A_n)). This is known as the monotone convergence theorem.

Which of the following is not a type of measure: Lebesgue measure, counting measure, or probability measure?

  1. Lebesgue measure

  2. Counting measure

  3. Probability measure


Correct Option: C
Explanation:

The correct answer is probability measure. A probability measure is a measure that assigns a value between 0 and 1 to a set, representing the probability of that set occurring.

Let (\mu) be a measure on a set (X). If (A) and (B) are sets in (X) such that (A \cap B = \emptyset), then what is the relationship between (\mu(A \cup B)) and (\mu(A) + \mu(B))?

  1. (\mu(A \cup B) = \mu(A) + \mu(B))

  2. (\mu(A \cup B) < \mu(A) + \mu(B))

  3. (\mu(A \cup B) > \mu(A) + \mu(B))


Correct Option: A
Explanation:

The correct answer is (\mu(A \cup B) = \mu(A) + \mu(B)). This is known as the additivity property of a measure.

Let (\mu) be a measure on a set (X). If (A_1, A_2, \ldots) is a sequence of sets in (X) such that (A_n \cap A_m = \emptyset) for all (n \neq m), then what is the relationship between (\mu(\cup_{n=1}^\infty A_n)) and (\sum_{n=1}^\infty \mu(A_n))?

  1. (\mu(\cup_{n=1}^\infty A_n) = \sum_{n=1}^\infty \mu(A_n))

  2. (\mu(\cup_{n=1}^\infty A_n) < \sum_{n=1}^\infty \mu(A_n))

  3. (\mu(\cup_{n=1}^\infty A_n) > \sum_{n=1}^\infty \mu(A_n))


Correct Option: A
Explanation:

The correct answer is (\mu(\cup_{n=1}^\infty A_n) = \sum_{n=1}^\infty \mu(A_n)). This is known as the countable additivity property of a measure.

Let (\mu) be a measure on a set (X). If (A) and (B) are sets in (X) such that (A \subseteq B), then what is the relationship between (\mu(A)) and (\mu(B))?

  1. (\mu(A) = \mu(B))

  2. (\mu(A) < \mu(B))

  3. (\mu(A) > \mu(B))


Correct Option: B
Explanation:

The correct answer is (\mu(A) < \mu(B)). This is known as the monotonicity property of a measure.

Let (\mu) be a measure on a set (X). If (A) is a set in (X) such that (\mu(A) = 0), then what is the relationship between (\mu(A \cup B)) and (\mu(B)) for any set (B) in (X)?

  1. (\mu(A \cup B) = \mu(B))

  2. (\mu(A \cup B) < \mu(B))

  3. (\mu(A \cup B) > \mu(B))


Correct Option: A
Explanation:

The correct answer is (\mu(A \cup B) = \mu(B)). This is known as the zero measure property of a measure.

Let (\mu) be a measure on a set (X). If (A_1, A_2, \ldots) is a sequence of sets in (X) such that (A_n \downarrow A) (i.e., (A_1 \supseteq A_2 \supseteq \cdots) and (\cap_{n=1}^\infty A_n = A)), then what is the relationship between (\mu(A_n)) and (\mu(A))?

  1. (\mu(A_n) = \mu(A))

  2. (\mu(A_n) < \mu(A))

  3. (\mu(A_n) > \mu(A))


Correct Option:
Explanation:

The correct answer is (\mu(A_n) \downarrow \mu(A)). This is known as the monotone convergence theorem.

Let (\mu) be a measure on a set (X). If (A_1, A_2, \ldots) is a sequence of sets in (X) such that (A_n \uparrow A) (i.e., (A_1 \subseteq A_2 \subseteq \cdots) and (\cup_{n=1}^\infty A_n = A)), then what is the relationship between (\mu(A_n)) and (\mu(A))?

  1. (\mu(A_n) = \mu(A))

  2. (\mu(A_n) < \mu(A))

  3. (\mu(A_n) > \mu(A))


Correct Option:
Explanation:

The correct answer is (\mu(A_n) \uparrow \mu(A)). This is known as the monotone convergence theorem.

Let (\mu) be a measure on a set (X). If (A) and (B) are sets in (X) such that (\mu(A) = \mu(B)), then what is the relationship between (\mu(A \cup B)) and (\mu(A \cap B))?

  1. (\mu(A \cup B) = \mu(A \cap B))

  2. (\mu(A \cup B) < \mu(A \cap B))

  3. (\mu(A \cup B) > \mu(A \cap B))


Correct Option:
Explanation:

The correct answer is (\mu(A \cup B) = \mu(A) + \mu(B) - \mu(A \cap B)). This is known as the inclusion-exclusion principle.

Let (\mu) be a measure on a set (X). If (A) is a set in (X) such that (\mu(A) = 1), then what is the relationship between (\mu(A \cap B)) and (\mu(B)) for any set (B) in (X)?

  1. (\mu(A \cap B) = \mu(B))

  2. (\mu(A \cap B) < \mu(B))

  3. (\mu(A \cap B) > \mu(B))


Correct Option: A
Explanation:

The correct answer is (\mu(A \cap B) = \mu(B)). This is known as the dominated convergence theorem.

Let (\mu) be a measure on a set (X). If (A) and (B) are sets in (X) such that (\mu(A) = \mu(B) = \infty), then what is the relationship between (\mu(A \cup B)) and (\mu(A \cap B))?

  1. (\mu(A \cup B) = \mu(A \cap B))

  2. (\mu(A \cup B) < \mu(A \cap B))

  3. (\mu(A \cup B) > \mu(A \cap B))


Correct Option:
Explanation:

The correct answer is (\mu(A \cup B) = \infty). This is known as the sigma-additivity property of a measure.

Let (\mu) be a measure on a set (X). If (A_1, A_2, \ldots) is a sequence of sets in (X) such that (\mu(A_n) \to 0) as (n) approaches infinity, then what is the relationship between (\mu(\cup_{n=1}^\infty A_n)) and (0)?

  1. (\mu(\cup_{n=1}^\infty A_n) = 0)

  2. (\mu(\cup_{n=1}^\infty A_n) < 0)

  3. (\mu(\cup_{n=1}^\infty A_n) > 0)


Correct Option: A
Explanation:

The correct answer is (\mu(\cup_{n=1}^\infty A_n) = 0). This is known as the Borel-Cantelli lemma.

Let (\mu) be a measure on a set (X). If (A) and (B) are sets in (X) such that (\mu(A) = \infty) and (\mu(B) = 0), then what is the relationship between (\mu(A \cup B)) and (\mu(A))?

  1. (\mu(A \cup B) = \mu(A))

  2. (\mu(A \cup B) < \mu(A))

  3. (\mu(A \cup B) > \mu(A))


Correct Option:
Explanation:

The correct answer is (\mu(A \cup B) = \infty). This is known as the sigma-additivity property of a measure.

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