Problem 2. Do the following for the function f: R²R given by f(x, y) = 1² + y (a) For A = {(-1,0), (0, 1), (1,0), (2, 1)}, list the elements of f(4). (b) What is f(R²)? Is it all of R or something else?

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Definition.** Let \( f : X \to Y \) and \( A \subset X \). The **direct image** of \( A \) under \( f \) is the set
\[ f(A) = \{ y \in Y \mid \exists a \in A \text{ such that } f(a) = y \}. \]

**Remark.** Another way to define the direct image of \( A \) under \( f \) is as the set
\[ f(A) = \{ f(a) \mid a \in A \}. \]

---

**Problem 2.** Do the following for the function \( f : \mathbb{R}^2 \to \mathbb{R} \) given by \( f(x, y) = x^2 + y^2 \).

(a) For \( A = \{(-1,0), (0,1), (1,0), (2,1)\} \), list the elements of \( f(A) \).

(b) What is \( f(\mathbb{R}^2) \)? Is it all of \( \mathbb{R} \) or something else?

---

**Problem 3.** Let \( f : X \to Y \), and \( A \) and \( B \) be subsets of \( X \). Prove the following statements.

(a) If \( A \subset B \), then \( f(A) \subset f(B) \).

(b) \( f(A \cap B) \subset f(A) \cap f(B) \).
Transcribed Image Text:**Definition.** Let \( f : X \to Y \) and \( A \subset X \). The **direct image** of \( A \) under \( f \) is the set \[ f(A) = \{ y \in Y \mid \exists a \in A \text{ such that } f(a) = y \}. \] **Remark.** Another way to define the direct image of \( A \) under \( f \) is as the set \[ f(A) = \{ f(a) \mid a \in A \}. \] --- **Problem 2.** Do the following for the function \( f : \mathbb{R}^2 \to \mathbb{R} \) given by \( f(x, y) = x^2 + y^2 \). (a) For \( A = \{(-1,0), (0,1), (1,0), (2,1)\} \), list the elements of \( f(A) \). (b) What is \( f(\mathbb{R}^2) \)? Is it all of \( \mathbb{R} \) or something else? --- **Problem 3.** Let \( f : X \to Y \), and \( A \) and \( B \) be subsets of \( X \). Prove the following statements. (a) If \( A \subset B \), then \( f(A) \subset f(B) \). (b) \( f(A \cap B) \subset f(A) \cap f(B) \).
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