# Quod Erat Demonstrandum

## 2011/09/30

### [FW][vimeo] Mathematics is my life!

Filed under: Fun — johnmayhk @ 5:55 上午

## 2011/09/24

### [FW] Surprises in Mathematics

Filed under: Fun — johnmayhk @ 6:14 上午

Featuring Dr. Stan Wagon Professor of Mathematics – Macalester College. There is no better way to get someone’s attention than with an assertion that just seems obviously wrong. Math is full of such things. The talk presents several surprising even shocking things from elementary mathematics such as: A square wheel that rolls perfectly smoothly. A device that uses a normal rotating crankshaft to drill perfect square holes. An application of a non-circular wheel to sewage disposal. A shocking cake puzzle. Surprising new formulas for π. Benford’s mysterious law of first digits. The Banach-Tarski Paradox with constructible pieces.

http://www.viddler.com/explore/uncasheville/videos/60/

http://www.viddler.com/explore/uncasheville/videos/61/

## 2011/09/23

### second fundamental theorem of calculus

Filed under: HKALE,Pure Mathematics,Teaching — johnmayhk @ 11:42 上午

$\frac{d}{dx}\int_a^xf(t)dt=f(x)$

（其中 $f$ 在開區間 $I$ 內連續，$a\in I$ 是常數。）

$\frac{d}{dx}\int_0^x(x-t)^2dt$ 是甚麼？ (more…)

## 2011/09/19

### (x=2 or x=-2) implies x^2=-4?

Filed under: Junior Form Mathematics,NSS — johnmayhk @ 4:11 下午

Just a question asked by a student, Thomas.

$x=2$
$x=-2$

multiply the above, yield

$x^2=-4$

strange?

He puzzled that, why (more…)

## 2011/09/08

### 食數

Filed under: Fun — johnmayhk @ 6:09 上午

http://wusa9.com/news/article/165892/373/Helping-Kids-Love-Math-By-Eating-It

## 2011/09/06

### Can you draw…

Filed under: NSS — johnmayhk @ 5:57 上午
Tags:

Can you draw a triangle with area of 100 $cm^2$, and two of its sides are 10 cm and 16 cm long? Explain briefly.

（在絕對平面上）理論上，是畫不到的。因為

$100=\frac{1}{2}(10)(16)\sin \theta$

### 驃叔語錄

Filed under: Life — johnmayhk @ 5:30 上午

（圖片來源：顏冊轉載）

http://zh.wikipedia.org/wiki/%E8%91%A3%E9%A9%83

## 2011/09/03

### [FW] Quants: The Alchemists of Wall Street (Marije Meerman, VPRO Backlight 2010)

Filed under: Fun — johnmayhk @ 3:20 下午