Exercise · ZW-MEASURABLE-FUNCTION-004 · ★☆☆ Basic
What kind of set is the preimage \(f^{-1}((a,\infty))\) when f is measurable?
Choose one option.
Show answer
- A. A measurable set
Explanation
If f is measurable, every Borel preimage belongs to the σ-algebra, so it is measurable. It need not be finite, empty or of measure zero.
Review the concept: Measurable function
A function f: X → ℝ is measurable with respect to a σ-algebra \(\mathcal{A}\) on X if the preimage \(f^{-1}(B)\) belongs to \(\mathcal{A}\) for every Borel set B of ℝ.
\[f^{-1}(B)\in\mathcal{A}\ \forall B\in\mathcal{B}(\mathbb{R})\]
More practice problems: measurable function
- ZW-MEASURABLE-FUNCTION-001 What is the name of the condition satisfied by f when f^-1(B) lies in A for every Borel B?
- ZW-MEASURABLE-FUNCTION-002 Which σ-algebra is usually used on ℝ to define measurability of real functions?
- ZW-MEASURABLE-FUNCTION-003 Which of these functions from ℝ to ℝ is NOT measurable with respect to the Borel σ-algebra?
- ZW-MEASURABLE-FUNCTION-005 Is every continuous function from ℝ to ℝ measurable with respect to the Borel σ-algebra?
- ZW-MEASURABLE-FUNCTION-006 Let f(x)=begincases1 & x≥ 0\\ 0 & x<0endcases on ℝ. What is f^-1((1/2,∞))?
- ZW-MEASURABLE-FUNCTION-007 Let f_n(x)=x^n on [0,1]. What is the pointwise limit f and why is it measurable?
- ZW-MEASURABLE-FUNCTION-008 If f and g are measurable, why is f+g measurable?
- ZW-MEASURABLE-FUNCTION-009 Let f be measurable with f^-1((a,∞))inA for all a∈ℝ. What does this imply about f^-1([a,∞))?