Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**Monox D. I-Fly****Member**- Registered: 2015-12-02
- Posts: 926

Weeks ago I had a job to edit a mathematic encyclopedia. When I needed to prove something, I did it using steps similar to ~(p ^ q ^ r) ≡ ~p ∨ ~q ∨ ~r. However, when my co-worker which is also a mathematic education graduate just like me doubted me because as far as she knew, De Morgan's law taught at school and college only consisted of two statements yet I applied it to three statements. I have explained that De Morgan's law still applied for three sentences because the two logical operations within the brackets are the same, but she still didn't believe it. Then I went easy on here by replacing that step with another method and showed that after a few steps I still got the same result as before, but she got confused. According to you guys, is De Morgan's law really only applicable to two statements?

Offline

No, De Morgan's law still holds for 3 statements. In fact, it's even applicable to an (uncountably) infinite number of statements. If you're having doubts, just let S = Q ^ R and use De Morgan's law for 2 statements. (Though it sounds like you've already done that.)

*Last edited by zetafunc (2016-01-05 12:08:38)*

**LearnMathsFree: Videos on various topics.New: Integration Problem | Adding FractionsPopular: Continued Fractions | Metric Spaces | Duality**

Offline

**Monox D. I-Fly****Member**- Registered: 2015-12-02
- Posts: 926

Well, this morning I tried to explain that to her. Thankfully she understood my explanation.

Offline

Pages: **1**