Timeline for Examples of interesting false proofs
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 7 at 18:46 | comment | added | Sayan Dutta | Wait till you see this : link.springer.com/article/10.1007/s12045-024-1737-2 | |
| Jan 10, 2019 at 15:20 | comment | added | Gerry Myerson | Those who were as mystified by cheval/oiseau may find enlightenment at algorythmes.blogspot.com/2009/09/cheval-oiseau-pi.html When that link disappears, just type cheval/oiseau = pi into (whatever search engine has replaced) Google. | |
| Dec 11, 2014 at 17:43 | comment | added | Denis Serre | In the same vein, one "proves" in French the equality $\frac{\rm cheval}{\rm oiseau}=\pi$. Read $\frac{\rm horse}{\rm bird}=\pi$, although there is no such proof in English. | |
| Jul 6, 2014 at 11:21 | comment | added | thomashennecke | A friend of mine once showed me this one, which had been copied by some biologists he was marking: $sin(mx + \pi /2)/sin(mx - \pi/2) = (mx + \pi /2)/(mx - \pi/2) = \pi/2 / - \pi/2 = -1$ | |
| Jun 16, 2012 at 15:25 | comment | added | Toby Bartels | My algebra students know better than to fall for this, but they will try to reduce $\frac{x+3}{x+4}$ to $\frac{3}{4}$. So then I invoke this, asking them if $\frac{13}{14}$ reduces to $\frac{3}{4}$, and (when they say No) asking them what happens when $x := 10$. | |
| Apr 22, 2012 at 21:24 | comment | added | Doug Chatham | For more examples and analysis of these "weird fractions", see A Pumping Lemma for Invalid Reductions of Fractions, Michael N. Fried and Mayer Goldberg, The College Mathematics Journal, Vol. 41, No. 5 (November 2010), pp. 357-364. | |
| Apr 21, 2012 at 19:59 | comment | added | Noam D. Elkies | Likewise $19/95 = 1/5$, $26/65 = 2/5$, and (a bit less satisfactory because not in lowest terms) $49/98 = 4/8$. | |
| Apr 21, 2012 at 15:06 | comment | added | Donu Arapura | This reminds me of a student in one of my classes who simplified $\frac{\sin x}{n} = six$. I almost gave him credit for that. | |
| Apr 21, 2012 at 14:49 | history | answered | Karl Schwede | CC BY-SA 3.0 |