Math Problem Statement

Which of these functions defines one-to-one correspondence from (0, 2) to (3, ∞)?

A) 2/π‘₯ + 2 B) 3/x + 3

C) 1/x + 2

D) 1/x + 3

E) None of the mentioned

Solution

To determine which of these functions defines a one-to-one correspondence (bijection) from the domain (0,2)(0, 2) to the range (3,∞)(3, \infty), we analyze the behavior of each function.

Step 1: Criteria for One-to-One Correspondence

  • Injective (One-to-One): Each xx in the domain maps to a unique yy in the range.
  • Surjective (Onto): Every value in the range (3,∞)(3, \infty) must be reachable from some xx in the domain (0,2)(0, 2).

Step 2: Analyze Each Function

A) f(x)=2x+2f(x) = \frac{2}{x} + 2

  1. Domain Check: For x∈(0,2)x \in (0, 2), f(x)f(x) is defined.
  2. Range Check:
    • As xβ†’0+x \to 0^+, 2xβ†’βˆž\frac{2}{x} \to \infty, so f(x)β†’βˆžf(x) \to \infty.
    • As xβ†’2βˆ’x \to 2^-, 2xβ†’1\frac{2}{x} \to 1, so f(x)β†’3f(x) \to 3.
    • Range: (3,∞)(3, \infty).
  3. f(x)f(x) is strictly decreasing (derivative is negative), ensuring injectivity.

This function is a bijection.


B) f(x)=3x+3f(x) = \frac{3}{x} + 3

  1. Domain Check: For x∈(0,2)x \in (0, 2), f(x)f(x) is defined.
  2. Range Check:
    • As xβ†’0+x \to 0^+, 3xβ†’βˆž\frac{3}{x} \to \infty, so f(x)β†’βˆžf(x) \to \infty.
    • As xβ†’2βˆ’x \to 2^-, 3xβ†’32\frac{3}{x} \to \frac{3}{2}, so f(x)β†’32+3=4.5f(x) \to \frac{3}{2} + 3 = 4.5.
    • Range: (4.5,∞)(4.5, \infty).
  3. Since (4.5,∞)β‰ (3,∞)(4.5, \infty) \neq (3, \infty), this is not surjective.

Not a bijection.


C) f(x)=1x+2f(x) = \frac{1}{x} + 2

  1. Domain Check: For x∈(0,2)x \in (0, 2), f(x)f(x) is defined.
  2. Range Check:
    • As xβ†’0+x \to 0^+, 1xβ†’βˆž\frac{1}{x} \to \infty, so f(x)β†’βˆžf(x) \to \infty.
    • As xβ†’2βˆ’x \to 2^-, 1xβ†’12\frac{1}{x} \to \frac{1}{2}, so f(x)β†’2.5f(x) \to 2.5.
    • Range: (2.5,∞)(2.5, \infty).
  3. Since (2.5,∞)β‰ (3,∞)(2.5, \infty) \neq (3, \infty), this is not surjective.

Not a bijection.


D) f(x)=1x+3f(x) = \frac{1}{x} + 3

  1. Domain Check: For x∈(0,2)x \in (0, 2), f(x)f(x) is defined.
  2. Range Check:
    • As xβ†’0+x \to 0^+, 1xβ†’βˆž\frac{1}{x} \to \infty, so f(x)β†’βˆžf(x) \to \infty.
    • As xβ†’2βˆ’x \to 2^-, 1xβ†’12\frac{1}{x} \to \frac{1}{2}, so f(x)β†’3.5f(x) \to 3.5.
    • Range: (3.5,∞)(3.5, \infty).
  3. Since (3.5,∞)β‰ (3,∞)(3.5, \infty) \neq (3, \infty), this is not surjective.

Not a bijection.


E) None of the mentioned

Since f(x)=2x+2f(x) = \frac{2}{x} + 2 satisfies the conditions for a bijection from (0,2)(0, 2) to (3,∞)(3, \infty), this option is incorrect.


Final Answer:

A) f(x)=2x+2f(x) = \frac{2}{x} + 2


Do you want a detailed explanation for any specific step?

Here are 5 related questions to explore:

  1. How do you verify if a function is strictly increasing or decreasing?
  2. What are the conditions for a function to be bijective?
  3. Can you find the derivative of f(x)=2x+2f(x) = \frac{2}{x} + 2 and interpret it?
  4. Why do functions like f(x)=1x+3f(x) = \frac{1}{x} + 3 fail to map onto (3,∞)(3, \infty)?
  5. What changes in the function domain or codomain would make f(x)=1x+3f(x) = \frac{1}{x} + 3 bijective?

Tip: Always test the limits of a function at the boundaries of its domain to verify its range.

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Math Problem Analysis

Mathematical Concepts

Functions
One-to-One Correspondence
Domain and Range
Injective and Surjective Functions

Formulas

f(x) = 2/x + 2
f(x) = 3/x + 3
f(x) = 1/x + 2
f(x) = 1/x + 3

Theorems

Criteria for bijection: A function must be both injective (one-to-one) and surjective (onto).
Behavior of functions near domain boundaries to determine range.

Suitable Grade Level

Grades 11-12