Symmetry
Line symmetry, where folding along the axis makes the two halves match exactly; deciding whether common shapes are symmetric and counting their axes, such as 2 for a rectangle, 4 for a square and countless for a circle; why a rectangle's diagonals are not axes; folding and cutting paper; and completing a symmetric shape on squared paper and finding symmetric points.
Key words
| Chinese | English |
|---|---|
| 軸對稱圖形 | line-symmetric shape |
| 對稱軸 | axis of symmetry |
| 對摺 | fold in half |
| 重合 | match exactly |
| 對稱點 | symmetric point |
The 5 short lessons and the chapter test
Lessons are in Chinese for now.
- 認識軸對稱圖形
- 對稱軸的數目
- 對摺、剪紙和補畫
- 對稱點
- 重溫
- 章節測驗 (chapter test)
Sample questions (in Chinese)
Question 1這句話對還是錯？
這個長方形是軸對稱圖形。
- 對
- 錯
Answer and explanation
答案：A．對
為甚麼？沿對稱軸對摺，長方形的兩邊能完全重合，所以是軸對稱圖形。長方形有 2 條對稱軸。
Question 2這句話對還是錯？
圖中的紅色虛線是這個長方形的對稱軸。
- 錯
- 對
Answer and explanation
答案：B．對
為甚麼？沿虛線對摺，兩邊能完全重合，所以虛線是對稱軸。
Question 3這個正方形有多少條對稱軸？
條
Answer and explanation
答案：4 條
為甚麼？正方形有 4 條對稱軸。兩條經過對邊的中點，兩條是對角線。
Question 4下面哪一個圖形是軸對稱圖形？
- 不等邊三角形
- 平行四邊形
- 直角梯形
- 等腰梯形
Answer and explanation
答案：D．等腰梯形
為甚麼？等腰梯形有 1 條對稱軸，是軸對稱圖形。其他的都不是軸對稱圖形。
Based on learning unit 6S1 of the Education Bureau’s Primary Mathematics Curriculum (2017).