Introduction to Geometry

1. Form 1 Mathematics Chapter 6 Introduction to Geometry

2. Reminder • SHW (III), Re-dictation & OBQ • Today • SHW (I), Dictation, Re-dictation Correction • 1 Feb (Fri) • SHW (II), (III), Drawing, OBQ Correction, Bring Textbook, Workbook 1B • 4 Feb (Mon) • CBQ • 6 Feb (Wed)

3. Dictation Answers • Here are the answers: • 1. 線段 Line Segment • 2. 頂點 Vertex • 3. 平行線 Parallel Lines • 4. 垂直線 Perpendicular Lines • 5. 鈍角 Obtuse Angle • 6. 等腰三角形 Isosceles Triangle

4. Dictation Answers • Next we have: • 7. 圓周 Circumference • 8. 直徑 Diameter • 9. 對角線 Diagonal • 10. 正多邊形 Regular Polygon • 11. 等邊五邊形 Equilateral Pentagon • 12.等角六邊形 Equiangular Hexagon • Correction: 10 times

5. Re-Dictation • Give the English name of the followings: • 1. 銳角 • 2. 反角 • 3. 平面圖形 • 4. 曲面 • 5. 半徑 • 6. 相交

6. Re-Dictation • Give the English name of the followings: • 7.四邊形 • 8. 多面體 • 9. 等距畫圖 • 10. 均勻橫切面 • 11.等邊三角形 • 12. 全等八角形 • Can you get them all?

7. Re-Dictation Answers • Here are the answers: • 1. 銳角 Acute angle • 2. 反角 Reflex angle • 3. 平面圖形 Plane figure • 4. 曲面 Curved surface • 5. 半徑 Radius • 6. 相交 Intersect

8. Re-Dictation Answers • Next we have: • 7.四邊形 Quadrilateral • 8. 多面體 Polyhedron / Polyhedra • 9. 等距畫圖 Isometric drawing • 10. 均勻橫切面 Uniform cross-section • 11.等邊三角形 Equilateral triangle • 12. 全等八角形 Regular octagon • Can you get them all?

9. Points, Lines and Planes • Points 點 • Lines 線 • Planes 面

10. Angles • Angles: • Name of angles (middle letter is vertex!)

11. Types of Angles (p.229) • There are six types:

12. Parallel lines (p.231) • When two lines in the same plane, but they do not intersect each other, they are called parallel lines (平行線) • A pair of parallel lines is denoted by a pair of arrows (箭號) • We write “AB//CD”

13. Perpendicular lines (p.232) • When two lines in the same plane are intersecting at right angle (90), they are called perpendicular lines (垂直線) • A right angle willbe clearly shownin a pair of perpendicular lines • We write “ABCD”

14. Plane Figure (p.235) • Any shape enclosed by line segments in the same plane is called Plane Figure. • Otherwise, it should be a curved surface.

15. Polygons (多邊形) (p.242) • The name of the polygons depends on the number of straight lines: • Triangle 3 lines (Tri-) • Quadrilateral 4 lines (Quadri-) • Pentagon 5 lines (Penta-) • Hexagon 6 lines (Hexa-) • Octagon 8 lines (Octa-) • Number prefix (from wikipedia)

16. Polygons (多邊形) (p.242) • Diagonal (對角線) is the line segment joining any two non-adjacent (不相鄰) vertices(頂點vertex) • A line segment joining two adjacent vertices is called a side (邊) • Same side  Equilateral (等邊)polygon • Same angle  Equiangular (等角) polygon • Both  Regular polygon(正多邊形)

17. C r d Circle (p.235) • All points on the circle (circumference 圓周) are at the same distance (radius半徑) from the a fixed point (centre 圓心). • Diameter (直徑) is 2 x Radius (d = 2r) • C = d x  (圓周率)or C = 2r •   3.14159 26535 897…

18. Types of Triangle (p.237) • Triangles are formed by three straight lines • Its name depends on its angles

19. Angle Sum of a Triangle • Sum of angles of a triangle is 180 • a + b + c = 180 (Straight angle = 180)

20. SHW (II) Q.8(a) •  Sum of : a + b + c = 180

21. SHW (II) Q.8(b) •  Sum of : a + b + c = 180

22. Solids (p.247) • Solids are 3-D (three-dimensional) figures. Plane Vertex Curved surface Edge

23. 1 cm 1 cm 1 cm Drawing Solids • Dotted lines • Isometric Drawing

24. Cross-section • If we cut a solid at right angle to its length, the plane is called a cross-section. • If planes from the parallel cuts are the same, the plane is a uniform cross-section

25. Polyhedra (多面體) • When all faces of a solid are polygons only, it is called a polyhedron. Yes! No!

26. Model of Polyhedra • The connected planes of a polyhedron are called a net.

27. Reminder • Drawing Exercises & Dictation • Today!!!! • SHW (III) & OBQ • 30 Jan (Wed) • SHW (I), (II), Dictation Correction • 1 Feb (Fri) • SHW (III), OBQ Correction • 4 Feb (Mon) • CBQ • 6 Feb (Wed)

28. Enjoy the world of Mathematics! Ronald HUI