1) The document is a lesson plan for a junior high school mathematics class on similarity and congruence. 2) The lesson will focus on using the concept of similarity of triangles to solve problems, including determining the ratio of sides of similar triangles and calculating lengths. 3) Students will work in groups on worksheet problems, then presentations and discussions will help summarize the material.

1. LESSON PLAN
Level : Junior High School
Subject : Mathematics
Class : IX
Semester : I
Topic : Similarity and Congruence
Standard Competence : Understanding the similarity of
figures and the use of it in problem
solving
Time Allocation : 2 x 40 minutes
Standard Competence
Understanding the similarity of figures and the use of it in problem solving
Basic Competence
Using the concept of similarity of triangle in problem solving
Indicators
1. Determine the ratio of the side of two triangle that are similar and calculate its
length
2. Solve problem related with similarity of a triangle
Learning Objectives
1. Students are able to determine the ratio of the side of two triangle that are similar
and calculate its length
2. Students are able to solve problem related with similarity of a triangle
Learning Model
Learning Model : Class Discussion
Learning Approach : Direct Presentation

2. Learning Method : Lecture Method, Question-Answer Method
Learning Sources
Handbook
Learning Materials
White board and board markers
PowerPoint Presentation
Learning Activities
 Apperception (± 10 minutes)
1. Phase 1. Clarify aims and establish set
a. Teacher communicates the outlines of basic competence and
indicators that will be learnt.
b. Teacher leads students to recall the lesson that had been learnt in the
previous meeting.
c. Teacher prepares the material and sets students ready to learn.
 Main Activities (± 60 minutes)
1. Phase 2. Focus the discussion
a. Teacher divides the students into several groups that contains of 2-3
students in each group.
b. Teacher extends problems that will be discussed (as a worksheet).
c. Teacher gives time to students to solve the problem and discuss
with their group.
2. Phase 3. Hold the discussion
a. After all the students solve the problems, teacher starts the discussion.
b. Teacher asks 1 group to present their idea to the whole class by
writing the answer on the whiteboard.
c. The teacher asks the other group to give their opinion about their
friend’s answer by raising their hand.

3. a
b
24 30
8
8
4
15
d. In the middle of the discussion, teacher may also present his/her own
ideas to the class to keep the discussion alive.
3. Phase 4. End the discussion
a. Teacher gives feedback about the student’s answer.
b. After doing the discussion, students summarize the material that have
been discussed.
4. Phase 5. Debrief the discussion
a. Teacher asks students to examine their discussion and thinking
processes.
 Closure (± 10 minutes)
a. Teacher leads students to conclude what they have learned that day.
b. Teacher may also give homework for students to practice.
c. Teacher closes the lesson that day.
Assessment
Individual Assessment : Participation
Grouped Assessment : Worksheet, participation
1. Calculate the length of a and b.
2. State, with reasons, whether ΔABC is similar to ΔPQR and find the value of x.

4. 3. The figure shows two similar cones.
a. Find the value of x.
b. What is the ratio of the base circumference of the smaller cone to that of the big
cone?
4. A model of an apartment block is made to a scale of 1 : 50.
a. Find the actual height of the apartment block if its height on the model is 42
cm.
b. If the area of the hall of the apartment is 34 m², find the area of the hall on the
model.
c. If the area of a unit of the apartment is 1200 cm² on the model, find its actual
area in m².