# Formulae 公式

Refer to the last chapter for symbol representation.

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$$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 $C=2\pi r=\pi d$.

# Techniques 技巧

When we meet irregular shapes, we can ‘move’ their perimeter without changing it’s value, as below. Note by Jeff Giff
1 month, 3 weeks ago

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

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

- 1 month, 3 weeks ago

Nope.

- 1 month, 3 weeks ago

Sorry :/

- 1 month, 3 weeks ago

That's okay.

- 1 month, 3 weeks ago