# Quod Erat Demonstrandum

## 2020/05/21

### Similar-looking formula

Filed under: Junior Form Mathematics,mathematics,Physics — johnmayhk @ 4:01 下午
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The equivalent resistance $R$ of a parallel circuit

can be determined by

$\displaystyle \frac{1}{R}=\frac{1}{R_1}+\frac{1}{R_2}$.

A similar-looking formula found in a basic mathematics question involving parallel lines as shown below:

## 2019/05/10

### 線長乘積

Filed under: Pure Mathematics — johnmayhk @ 11:52 下午
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## 2017/12/25

### 等邊三角形

Filed under: Junior Form Mathematics,Pure Mathematics — johnmayhk @ 12:13 下午
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e.g. 1

## 2017/11/13

### 平行四邊形的條件

Filed under: Junior Form Mathematics — johnmayhk @ 12:38 下午
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## 2017/11/08

### 作正五邊形

Filed under: Additional / Applied Mathematics,Fun,Junior Form Mathematics — johnmayhk @ 10:49 上午
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## 2017/06/10

### 正多邊形方程

Filed under: Additional / Applied Mathematics,Fun,mathematics,NSS — johnmayhk @ 12:24 下午
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https://www.desmos.com/calculator/vv7stc4nl0

## 2017/01/10

### 某經典幾何題

Filed under: NSS,Pure Mathematics — johnmayhk @ 5:03 下午
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https://www.geogebra.org/m/WPk7sZUJ

（若有興趣知如何構作兩圓的外公共切線，可看文末的附錄*）

## 2016/08/29

### 講兩題

Filed under: Junior Form Mathematics,NSS — johnmayhk @ 5:02 下午
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（注：上圖式子是 $k^{th}$ moment 的定義。特別地，當 k=2，它就是方差 variance。）

（一）

$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$ (more…)

## 2016/06/14

### 正七邊形

Filed under: Fun — johnmayhk @ 12:07 上午
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（習題）從片中某些結果不難推出以下命題： (more…)

## 2015/11/12

### 無聊兩題

Filed under: Junior Form Mathematics,NSS — johnmayhk @ 9:39 下午
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1. 初中

## 2015/08/25

### 等邊三角形面積

Filed under: Junior Form Mathematics,NSS — johnmayhk @ 4:03 下午
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## 2015/07/14

### 某初中幾何題

Filed under: Junior Form Mathematics — johnmayhk @ 10:53 上午
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$c=\frac{6+12}{2}$

## 2015/05/20

### 幾何老題

Filed under: Fun — johnmayhk @ 1:40 下午
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$x$ 的大小。（圖有誤，$\angle ACD=30^o$，非 $60^o$

## 2015/03/07

### 幾條正三角形

Filed under: mathematics,NSS — johnmayhk @ 8:59 下午
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## 2013/07/07

### just an old file

Filed under: mathematics — johnmayhk @ 3:11 下午
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