Form 1 MathematicsChapter 11

Lesson requirement 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

Missing HW Detention

SHW (I) 8th May (Wednesday)

SHW (II) 14th May (Tuesday)

OBQ 15th May (Wednesday)

CBQ 20th May (Monday)

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.

2. Two congruent figures can fit exactly on each other.

X Y

Page 173 of Textbook 1B Class Practice

Pages 176 – 177 of Textbook 1B Questions 1 – 2

Page 73 of Workbook 1B Question 1

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

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.

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

Example 1:Name a pair of congruent triangles in the figure.

From the figure above,

we have △ABC △RQP.

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°

Example 3:Given that △PQS △RSQ,

find the unknowns s and r.

Since △PQS △RSQ,we have PQ = RSi.e. s = 8 cm

and RQS = PSQ = 70°

In △RSQ,45° + RQS + r = 180° 45° + 70° + r = 180°

115° + r = 180°

r = 65°

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

Enjoy the world of Mathematics!

Ronald HUI