Geometry: Shapes & Angles
幾何：形狀與角
Geometry is the study of shapes and angles. In this lesson you will learn the names of 2D and 3D shapes, the types of angles, and what symmetry means.
幾何是研究形狀和角的學問。在這一課，你會學習二維和三維形狀的名稱、角的種類，以及對稱的意思。
1 · 2D shapes
二維形狀
A 2D shape is flat. A triangle has 3 sides, a square has 4 equal sides, a rectangle has 4 sides with opposite sides equal, and a circle is perfectly round.
二維形狀是平面的。三角形有 3 條邊，正方形有 4 條相等的邊，長方形有 4 條邊（對邊相等），圓形是完全圓滑的。
2 · 3D shapes
三維形狀
A 3D shape has length, width and height. A cube has 6 square faces. A sphere is a ball shape. A cylinder has two circular ends. A cone has one circular base and a point.
三維形狀有長、闊和高。正方體有 6 個正方形面。球體是球形。圓柱體有兩個圓形端。圓錐體有一個圓形底和一個尖端。
2D shapes are flat; 3D shapes have height too.
二維形狀是平面的；三維形狀還有高度。
3 · Angles
角
An angle is formed where two lines meet. A right angle is exactly 90 degrees. An acute angle is less than 90 degrees. An obtuse angle is more than 90 degrees but less than 180 degrees.
角是由兩條線相交而成。直角是 90 度。銳角小於 90 度。鈍角大於 90 度但小於 180 度。
4 · Symmetry
對稱
A shape has symmetry if you can fold it in half and the two halves match exactly. The fold line is called the line of symmetry. A square has 4 lines of symmetry.
如果一個形狀可以對摺，兩半完全重疊，它就具有對稱性。摺線稱為對稱軸。正方形有 4 條對稱軸。
5 · Quick check
小測驗