Angles (degrees)
The degree (°) as the unit for angles, with a right angle as 90°; acute, right, obtuse, straight, reflex angles and the full turn; measuring with a protractor, centre on the vertex and reading the scale that starts at 0°; estimating angles; naming an angle with three letters such as ∠ABC; and turning clockwise and anticlockwise through an angle, with the eight compass directions.
Key words
| Chinese | English |
|---|---|
| 度 | degree (°) |
| 量角器 | protractor |
| 反角 | reflex angle |
| 平角 | straight angle |
| 周角 | full angle |
| 順時針 | clockwise |
| 逆時針 | anticlockwise |
The 4 short lessons and the chapter test
Lessons are in Chinese for now.
- 認識度和角的種類
- 用量角器量角和估計
- 反角、平角和周角
- 旋轉和比較
- 章節測驗 (chapter test)
Sample questions (in Chinese)
Question 1把一張圓形手工紙對摺 3 次，摺痕在中心形成的角是多少度？
°
Answer and explanation
答案：45°
為甚麼？一個圓周是 360°。對摺一次得 180°，對摺兩次得 90°，對摺三次得 45°。所以答案是 45°。
Question 2一個 180° 的角是甚麼角？
- 平角
- 周角
- 直角
- 鈍角
Answer and explanation
答案：A．平角
為甚麼？平角等於 180°。所以 180° 的角是平角。
Question 3用量角器量得這個角是多少度？
- 120°
- 70°
- 110°
- 80°
Answer and explanation
答案：B．70°
為甚麼？角的一條邊對準左邊，那是外圈的 0°，所以要讀外圈的刻度：70°。讀錯了另一圈會得到 110°。看看角是銳角還是鈍角，可以幫助檢查。
Question 4估計這個角的大小，最接近哪一個？
- 230°
- 20°
- 65°
- 120°
Answer and explanation
答案：B．20°
為甚麼？先看它是甚麼角：銳角（小於 90°）。再和 90°、180° 比較。這個角大約是 20°。
Based on learning unit 6M1 of the Education Bureau’s Primary Mathematics Curriculum (2017).