1. Congruence and Similarity
Form 1 Mathematics
Chapter 11

2. Reminder Lesson requirement Before lessons start
Textbook 1B
Workbook 1B
Notebook
Before lessons start
Desks in good order!
No rubbish around!
No toilets!
Keep your folder at home
Prepare for Final Exam

3. Reminder Missing HW SHW (I) SHW (II) OBQ CBQ Detention
8th May (Wednesday)
SHW (II)
14th May (Tuesday)
OBQ
15th May (Wednesday)
CBQ
20th May (Monday)

4. Congruence (全等, p.172) Congruent figures (全等圖形)
1. Figures having the same shape and size are called congruent figures.
e.g. Figures X and Y below are congruent figures. X Y
2. Two congruent figures can fit exactly on each other.

5. Time for Practice Page 173 of Textbook 1B
Class Practice
Pages 176 – 177 of Textbook 1B
Questions 1 – 2
Page 73 of Workbook 1B
Question 1

6. Transformation and Congruence (p.174)
We learnt transformations in Chapter 9:
Translation
Reflection
Rotation
Enlargement and Reduction
Which one will NOT change the shape?
Try Class Discussion on p.174

7. Transformation and Congruence (p.174)
1. When a figure is translated, rotated or reflected, the image produced is congruent to the original figure.
2. When a figure is reduced or enlarged, the image produced will not be congruent to the original one.

8. Congruent Triangles (全等三角形, p.175)
Symbol “  ” means “is congruent to”
When two triangles are congruent,
(i) their corresponding sides (對應邊) are equal,
(ii) their corresponding angles (對應角) are equal.
e.g. If △ABC  △XYZ, then
AB = XY,
BC = YZ,
CA = ZX,
A = X,
B = Y,
C = Z. A B C X Y Z

9. Congruent Triangles (p.175)
Example 1:
Name a pair of congruent triangles in the figure.
From the figure above, we have △ABC  △RQP.

10. Congruent Triangles (p.175)
Example 2:
Given that △ABC  △XYZ, find the unknowns x, b and y.
∵ The corresponding sides and corresponding angles of two congruent triangles are equal,
∴ x = 5 cm, b = 6 cm, y = 50°

11. Congruent Triangles (p.175)
Example 3:
Given that △PQS  △RSQ,
find the unknowns s and r.
Since △PQS  △RSQ,
we have PQ = RS
i.e s = 8 cm
and RQS = PSQ = 70°
In △RSQ,
45° + RQS + r = 180°
45° + 70° + r = 180°
115° + r = 180°
r = 65°

12. Time for Practice Page 176 of Textbook 1B
Class Practice
Pages 177 – 178 of Textbook 1B
Questions 4 – 17
Pages 74 – 75 of Workbook 1B
Questions 2 – 5

13. Enjoy the world of Mathematics!
Ronald HUI