Angles
What an angle is: two straight arms from one point; that the size of an angle depends on how far the arms open, not on how long they are; right, acute and obtuse angles, checked against the right angle of a set square; and perpendicular lines, including that the perpendicular is the shortest path from a point to a line.
Key words
| Chinese | English |
|---|---|
| 角 | angle |
| 直角 | right angle |
| 鋭角 | acute angle |
| 鈍角 | obtuse angle |
| 垂直 | perpendicular |
| 三角尺 | set square |
The 7 short lessons and the chapter test
Lessons are in Chinese for now.
- 認識角
- 排列角的大小
- 直角
- 鋭角和鈍角
- 鐘面上的角
- 垂直線和距離
- 重溫
- 章節測驗 (chapter test)
Sample questions (in Chinese)
Question 1哪一個角比較小？
- 乙
- 甲
Answer and explanation
答案：A．乙
為甚麼？角的大小要看兩條邊張開的程度，和邊的長短無關。角乙的兩條邊張開得比較小，所以角乙比較小。
Question 2這是甚麼角？
- 直角
- 鋭角
- 鈍角
Answer and explanation
答案：C．鈍角
為甚麼？鈍角比直角大，但比兩個直角小。這個角比直角大，是鈍角。
Question 3下面哪一個是鈍角？
Answer and explanation
答案：A
為甚麼？鈍角比直角大，但比兩個直角小。
Question 4鐘面顯示 1 時。時針和分針組成甚麼角？
- 直角
- 鈍角
- 鋭角
Answer and explanation
答案：C．鋭角
為甚麼？分針指着 12，時針指着 1。兩枝針張開的程度比直角小，是鋭角。
Based on learning unit 2S2 of the Education Bureau’s Primary Mathematics Curriculum (2017).