1) The document describes a lesson plan on similar triangles taught by instructor Lorie Jane L. Letada. 2) The lesson introduces similar triangles and how to use ratio and proportion to calculate unknown side lengths. It includes examples of setting up and solving similar triangle ratios. 3) Students watch a video demonstrating how similar triangles can be used with a mirror to measure the height of an object without climbing it. They then practice applying ratio and proportion to similar triangle problems.

1. Republic of the Philippines
CEBU TECHNOLOGICAL UNIVERSITY
Main Campus
Corner M.J. Cuenco Avenue and R. Palma Street, Cebu City
hhtp://www.cscst.ph e-mail: information@csct.ph
Tel. No. 416-6585, Telefax No. 256-3608
_____________________________________________________________________
Name: Lorie Jane L. Letada Instructor: Dr. Elena Cecilia P. Delos Reyes, Ed. D
Methodology: Inductive Date: October 13, 2014
Similar Triangles
Subject Matter
I. Objectives
At the end of the lesson, the students can:
1. Investigate the properties of similar triangles using their prior knowledge of ratio
and proportion.
2. Solve carefully the value of x in the pair of triangles using the ratio and proportion.
3. Apply the use of similar triangles to a sight tool in order to measure the distance
between or height of any tall object like flag pole, trees and building.
II. Subject Content
Topic: Similar Triangles
Reference: E-math; Orlando A. Oronce pp.67-70
http://www.mathopenref.com/similartriangles.html;
http://www.regentsprep.org/regents/math/geometry/gp11/Lsimilar.htm;
https://www.youtube.com/watch?v=WA2ney3n0wY
Materials: whiteboard, marker, visual aid, video
III. Procedures
A. Preparation
Teacher’s Activity Student’s Activity
-Good Afternoon Class!
-How’s your afternoon?
-Oh! That’s good!
-But before we start, kindly pick up pieces
of paper under your chair and arrange it
properly.
-So, is everybody here?
-Wow! Very good! Give yourself around of
applause for a perfect attendance.
- Okay class, try to look outside.
-Good Afternoon Ma’am!
-It’s fine!
- (Picking the trashes and arrange their
chair.)
-Yes. Ma’am!
- (Clapping their hands.)
- (Looking outside)

2. -What do you see?
-Okay, don’t answer in chorus. Raise your
hand.
- Yes, Miss!
-Flag pole! Very good!
-Yes, Mister.
-Building! Very good!
-Yes, Miss!
-Coconut trees! Very good!
-So class, have you ever try to wonder how
we will going to find the height of that trees,
flag pole or building without climbing it?
-Do you want to find out?
-Okay, let’s watch this video first and try to
determine how the man in the video
measures the height of the tree without
climbing it!
-Now, class, What do you think did the man
do to measure the height of the tree?
-Don’t answer me in chorus. Just raise your
hand! Yes Miss!
-Okay, he used tape measure to find the
distance between the mirror and the tree,
but how about the distance between him
and the mirror. Didn’t he find it using the
tape measure?
-So meaning to say?
-So what does it mean?
-Okay, that’s right, but I want specific
answer how the man found the height of the
tree without climbing it.
-Who have an idea?
-Okay, you’re almost there but I need the
-I see plants! Building! Sky! Flag pole!
Students! Food stool! Trees!
-(Raising their hands)
-I see flag pole!
-I see building!
-I see coconut trees!
-Is it possible Ma’am?
-Yes! (Answer in unison)
- (Watching the video attentively.)
(The video runs one minute and
eighteen seconds.)
-He used tape measure.
-He used mirror.
-He used himself.
-He used tape measure to find the
distance between the mirror and the
tree.
-He also used it.
- It is not only the tape measure
contributes in finding the height of the
tree.
-The man also contributes in finding the
height of the tree.
-Ma’am, he used cross multiplication
method.
-Ma’am, he used ratio and proportion in
finding the height of the tree.

3. specific one.
-Very Good! He used ratio and proportion in
finding the height of the tree.
-Class, have you still remember our
previous lesson in ratio and proportion?
-So, why does it seem you forget it?
Anyway, the video you have watched is the
application of ratio and proportion, but
class, it is not only the ratio and proportion
contributes in finding the height of the tree.
There is still one and we will going to find
what it is.
-Yes, Ma’am.
B. Presentation
-Okay, class! Look at the two
triangles on the board.
-What have you observed?
-Very good! Another one!
-Very good! So now, class, I have
another example here and observe
this carefully.
-So, class, what have observed in
this equation?
Looking on the board and observing the two pair
of triangles.)
Ex: 1
ABC ˜ DEF
-There is a small and big triangle.
-The side of the small triangle is twice the side
of the big triangle.
Ex: 2

4. -Very good and what does it trying to
tell us?
-So, in other word?
-Okay, that’s a good idea! So class I
have another example here.
- Given the side of the small triangle,
find the value of h which is the height
to tennis ball to the ground.
-So class, who want to answer on
the board.
-Okay. Can you explain in your
classmate how did you get that
answer?
-Very good! Everyone, give her a
round of applause.
-So now guys, who can give me the
generalization of our topic. Can you
give one property of similar
triangles?
-Very good! Or in other word the
corresponding angles are congruent.
Just like in the example no. 1, in
which <A=<D; <B = E; <C=<F.
-Okay, who can give me the other
-Side DF over side AC is equal to side DE
over side AB.
-In finding the value of x, you will use ratio
and proportion.
-In two similar triangles, the big one and the
small one, when the height of big triangle is
missing, we can use the ratio and proportion.
Example 3:
-Yes miss.
h/0.9 = 18/6
6h=0.9(18)
6h=16.2
h=16.2/6
h=2.7 m
(Student 1 explaining her answer.)
-Angles of two similar triangles are same
measurement.

5. property of similar triangles? Yes,
Mister.
-Very good! Or in other word, the
corresponding sides are all in the
same proportion.
-The sides of two similar triangles are in the
same proportion.
C. Application:
-So class, who want to answer the
problem on the board?
(Students raising their hands and
answer the problem on the board.)
-So to those who are sitting kindly
answer the problem on your paper.
Afterwards….
-Okay, kindly explain your answer.
(Students explain their answer.)
-So class do you have any
question?
1. 1.
2.
3.
4.
5.

6. IV. Testing/Evaluation
-Okay, kindly get your activity
notebook and answer the following.
-No cheating please!
Using the properties of similar triangle, find the
value of x.
1.
2.
3.
4.
5.
6.

7. V. Assignment
1. In an open field area, select an object whose height you cannot measure.
2. Lay a small mirror horizontally on the ground exactly 1 meter/yard in front of the
object.
3. Slowly walk backwards until you can just see the top of the object in the mirror.
Determine your distance from the mirror.
4. Measure the distance from the ground to your eye level.
5. Draw similar triangles representing this situation in the space below. Label the
diagram and indicate all known measurements with units.
So class this is the example illustration of your assignment.
Put this on a short bond paper and pass this on Monday so you have your weekends
to do the task. To those who want to watch the video again, this is the website
https://www.youtube.com/watch?v=31qq1zoQVHY. Do you have any clarification?