Math Problem Statement

The domain for variable x is the set of positive real numbers. Select the statement that correctly describes the proposition ∀x(x^2 ≥ x).

Solution

The question asks to analyze the proposition x(x2x)\forall x (x^2 \geq x), where the domain for xx is the set of positive real numbers, and to determine which statement correctly describes this proposition.

Proposition breakdown:

  • The expression x2xx^2 \geq x must hold for all xR+x \in \mathbb{R}^+ (all positive real numbers).
  • We need to test this inequality to see if it's true for all values or if there are any counterexamples.

Step 1: Simplifying the inequality

The inequality can be rewritten as: x2xx^2 \geq x Dividing both sides by xx (since x>0x > 0, division is valid): x1x \geq 1 Thus, the inequality x2xx^2 \geq x holds if and only if x1x \geq 1.

Step 2: Checking counterexamples

  • For x=1x = 1, we have 12=11^2 = 1, which satisfies the inequality.
  • For x=12x = \frac{1}{2}, we have (12)2=14\left( \frac{1}{2} \right)^2 = \frac{1}{4}, and 14<12\frac{1}{4} < \frac{1}{2}, so the inequality does not hold.

Thus, x=12x = \frac{1}{2} serves as a counterexample where the proposition is false.

Correct answer:

Since the proposition is false and x=12x = \frac{1}{2} is a counterexample, Option C is correct:

  • C: The proposition is false, and x=12x = \frac{1}{2} is a counterexample.

Would you like more details or have any further questions?


Here are five related questions to deepen your understanding:

  1. What happens if xx includes negative real numbers? How would that affect the inequality x2xx^2 \geq x?
  2. How does the behavior of quadratic functions influence inequalities like x2xx^2 \geq x?
  3. What would the proposition look like if xx were restricted to integers?
  4. What is the relationship between counterexamples and the validity of universal quantifiers like x\forall x?
  5. How do we solve inequalities that involve powers of xx?

Tip: When dealing with inequalities and universal quantifiers, always check for edge cases and counterexamples to confirm the proposition's truth value.

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Math Problem Analysis

Mathematical Concepts

Inequalities
Universal Quantifiers
Counterexamples

Formulas

x^2 ≥ x

Theorems

Universal quantifier (∀)

Suitable Grade Level

Grades 9-12