명제와 조건 연습문제 — Sundstrom, Mathematical Reasoning · 2.4절 · 1a번

Sundstrom, Mathematical Reasoning · 2.4절 · 1a번영어 원문

For each of the following, write the statement as an English sentence and then explain why the statement is false.

$\left(\exists x \in \mathbb{Q} \right) \left( x^2 - 3x - 7 = 0 \right)$ .

정답·풀이 보기 (영어 원문)

There exists a rational number $x$ such that $x^2 - 3x - 7 = 0$ . This statement is false since the solutions of the equation are $x = \dfrac{3 \pm \sqrt{37}}{2}$ , which are irrational numbers.

한 번 더 — 비슷한 문제Sundstrom, Mathematical Reasoning · 2.4절영어 원문

An integer $n$ is a multiple of 3 provided that there exists an integer $k$ such that $n = 3k$ .

Use the symbolic form of the definition of a multiple of 3 to complete the following sentence: “An integer $n$ is not a multiple of 3 provided that ….”

다 풀었으면 정답 확인

An integer $n$ is not a multiple of 3 provided that $\left( \forall k \in \mathbb{Z} \right) \left( n \ne 3k \right)$ .

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