Math Problem Statement

Which of the following statements are true? Select all that apply. Assume the domain of discourse is the set of real numbers.

A.

∃x such that x2=x+1

B.

∀x,x2≤x

C.

∀x,x2=0

D.

∃x such that x2≤x

Solution

Let's analyze each statement:

A. ∃x such that x² = x + 1

This asks if there exists a real number xx such that x2=x+1x^2 = x + 1. Rearrange the equation: x2x1=0x^2 - x - 1 = 0 The discriminant (Δ\Delta) is: Δ=(1)24(1)(1)=1+4=5\Delta = (-1)^2 - 4(1)(-1) = 1 + 4 = 5 Since Δ>0\Delta > 0, this quadratic equation has two real solutions. Therefore, this statement is true.


B. ∀x, x² ≤ x

This asks if for all real numbers xx, x2xx^2 \leq x. Rearrange: x2x0orx(x1)0x^2 - x \leq 0 \quad \text{or} \quad x(x - 1) \leq 0 The critical points are x=0x = 0 and x=1x = 1. Test intervals:

  1. For x(,0)x \in (-\infty, 0): x(x1)>0x(x - 1) > 0 (false).
  2. For x[0,1]x \in [0, 1]: x(x1)0x(x - 1) \leq 0 (true).
  3. For x(1,)x \in (1, \infty): x(x1)>0x(x - 1) > 0 (false).

Thus, this statement is false because it is not true for all xx.


C. ∀x, x² = 0

This asks if for all real numbers xx, x2=0x^2 = 0. Clearly, this is false because x2=0x^2 = 0 is only true when x=0x = 0. For other values of xx, x20x^2 \neq 0.


D. ∃x such that x² ≤ x

This asks if there exists a real number xx such that x2xx^2 \leq x. From the analysis in BB:

  • x2xx^2 \leq x is true for x[0,1]x \in [0, 1].
  • For example, x=0.5x = 0.5 satisfies x2=0.250.5x^2 = 0.25 \leq 0.5.

Thus, this statement is true.


Final Answer:

  • True: A, D
  • False: B, C

Would you like further details or a graph to visualize these solutions?
Here are some related questions you might find interesting:

  1. How do we solve quadratic inequalities like x2x0x^2 - x \leq 0?
  2. What is the significance of the discriminant (Δ\Delta) in quadratic equations?
  3. Can xnxx^n \leq x hold for all nn and xx?
  4. What are the differences between "for all" (\forall) and "there exists" (\exists)?
  5. How can graphing help verify solutions to these types of problems?

Tip: When dealing with inequalities, always analyze the critical points and test intervals.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Real Numbers
Quadratic Equations
Inequalities
Existential Quantifiers
Universal Quantifiers

Formulas

Quadratic equation: ax² + bx + c = 0
Discriminant formula: Δ = b² - 4ac
Inequality analysis: x(x - 1) ≤ 0

Theorems

Properties of quadratic equations
Solution of inequalities with critical points

Suitable Grade Level

Grades 10-12