Introduction to Geometry

1. Form 1 Mathematics Chapter 6 Introduction to Geometry

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

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

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

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

6. 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”

7. 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”

8. 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.

9. 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)

10. 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)

11. 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…

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

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

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

15. 1 cm 1 cm 1 cm Drawing Solids • Dotted lines • Isometric Drawing

16. 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

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

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

19. Dictation • Words on the PowerPoint files • 12 questions • Write down the answers one-by-one • Final minutes for revision • Are you ready?

20. Dictation • Give the English name of the followings: • 1. 線段 • 2. 頂點 • 3. 平行線 • 4. 垂直線 • 5. 鈍角 • 6. 等腰三角形

21. Dictation • Give the English name of the followings: • 7. 圓周 • 8. 直徑 • 9. 對角線 • 10. 正多邊形 • 11. 等邊五邊形 • 12.等角六邊形 • Can you get them all?

22. 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

23. 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 • Can you get them all?

24. 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)

25. Enjoy the world of Mathematics! Ronald HUI