Math Problem Statement

Semesta pembicaraan adalah himpunan bilangan-bilangan real. Tentukan nilai logikanya kalimat-kalimat di bawah ini.

Solution

The question asks to determine the logical values (truth or falsity) of each statement given that the universe of discourse is the set of real numbers. Let's analyze each statement:

a. (x)2x+1=2x(\forall x) \, 2x + 1 = 2x

  • This statement means that for all xx, the equation 2x+1=2x2x + 1 = 2x must hold. Simplifying the equation: 2x+1=2x    1=02x + 1 = 2x \implies 1 = 0 This is clearly false for all real numbers. Hence, the statement is false.

b. (x)2x+1=2x(\exists x) \, 2x + 1 = 2x

  • This statement means that there exists some xx such that 2x+1=2x2x + 1 = 2x. From the analysis in part (a), we know that the equation reduces to 1=01 = 0, which is impossible for any real number. Therefore, this statement is also false.

c. (x)x=x(\forall x) \, |x| = x

  • This statement asserts that for all xx, x=x|x| = x. We know that: x=xonly ifx0|x| = x \quad \text{only if} \quad x \geq 0 However, for negative xx, x=x|x| = -x, so the statement does not hold for all real numbers. Therefore, this statement is false.

d. (x)x=x(\exists x) \, |x| = x

  • This means there exists at least one xx such that x=x|x| = x. This is true for any x0x \geq 0. For example, x=1x = 1 satisfies this condition. Therefore, this statement is true.

e. (x)x=0(\exists x) \, |x| = 0

  • This means there exists an xx such that x=0|x| = 0. We know that x=0|x| = 0 only if x=0x = 0. Therefore, this statement is true since x=0x = 0 satisfies the condition.

f. (x)x2=x(\exists x) \, x^2 = x

  • This means there exists an xx such that x2=xx^2 = x. Simplifying the equation: x2=x    x(x1)=0x^2 = x \implies x(x - 1) = 0 So, x=0x = 0 or x=1x = 1. Since there are solutions, the statement is true.

Summary of Results:

a. False
b. False
c. False
d. True
e. True
f. True


Would you like more details on any of these solutions or have any other questions?

Here are 5 related questions to expand on the concepts:

  1. What is the difference between universal and existential quantifiers in logic?
  2. How do absolute values affect equations with variables?
  3. Can you explain why x=x|x| = x is true only for non-negative values of xx?
  4. How can we solve equations involving x2=xx^2 = x and similar quadratic forms?
  5. What are the implications of contradictory statements like 2x+1=2x2x + 1 = 2x in logical reasoning?

Tip: When solving logical statements, always pay close attention to whether the statement is universal (applies to all values) or existential (applies to at least one value).

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Math Problem Analysis

Mathematical Concepts

Logic
Quantifiers
Algebra
Absolute Value
Real Numbers

Formulas

|x| = x if x >= 0
x^2 = x
2x + 1 = 2x leads to 1 = 0 (contradiction)

Theorems

Universal Quantifier (∀)
Existential Quantifier (∃)

Suitable Grade Level

Grades 10-12