# Formulae 公式

## quadrilaterals 四边形

Refer to the last chapter for symbol representation.

字母含义见上一章。

Square and rhombus 正方形和菱形: $4s$

Rectangle and parallelogram 长方形和平行四边形: $2(a+b)$ ($a$ and $b$ refer to the side length of two adjacent sides) （$a$ 和 $b$ 分别指两相邻边的长度）

## ellipticals 椭圆形

Call a circle’s circumference (perimeter) $C$ and diameter $d$. Then $\pi =\dfrac {C}{d}$, so $C=2\pi r=\pi d$.

将一个圆的圆周和直径的长度分别称为 $C$ 和 $d$ 。易得 $C=2\pi r=\pi d$ 。

# Techniques 技巧

When we meet irregular shapes, we can ‘move’ their perimeter without changing it’s value, as below.

当我们遇到不规则图形时，可以在不改边其周界长度当情况下边換其周界，如下。
Image 1.1.2-1 图1.1.2-1

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## Comments

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TopNewestJeff, this is good, but I don't understand Chinese.

Is there any other languages apart from Chinese and English that you can speak?

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Nope.

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Sorry :/

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That's okay.

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