1. Lesson Plan in Mathematics
I. Objectives
a. State the formula for finding the area of triangle;
b. Draw and illustrate the area of given triangle and;
c. Cooperate in all activities.
II. Subject Matter:
a. Topic: Deriving a formula for finding the area of triangle
b. Reference: Grade School Mathematics V p. 230-231
c. Materials: Cut outs of rectangle and triangle, learning activity sheets
III. Procedure:
A. Preparatory Activities
1. Mental Exercise
What shape do we have on the board?
How many triangles are these on the board?
How about in this figure? How many different triangles can you find?
How about in this figure?
2. Motivation
Our barangay fiesta here in Nancayasan is getting near isn’t class?
Since our fiesta is getting near, Diola bought a piece of colored paper 10
decimeters long and 6 decimeters wide. She cut diagonally to make 2 pieces
of pennants for the barrio fiesta parade. What is the area of each piece?
What do the people do during the fiesta?
What do they usually prepare?
Are flag lets important during fiestas?
Why?
B. Developmental Activities
1. Presentation
What did Diolea do the piece of colored paper?
What figure were form if she cut it diagonally?
Do you know the area of this figure?
So today, we are going to discuss on how to find the area of the triangle.
This is the colored paper bought by Diolea.

2. How did she cut again the colored paper class?
6 dm
10 dm
What is the measurement of the cloth?
Now this is the half part of the cloth.
6 dm
10 dm
The formula in finding area of the triangle is:
A=1/2 x (bxh) or A=bxh/2
What is asked in our problem?
Solution in finding the Area of a Triangle:
A=1/2 x (bxh)
A=1/2 x (10 dm x 6 dm)
A= ½ x 60 dm2
A=30 sq dm or 30 dm2
The area of the triangle is 30 sq dm or 3o dm2
We have another example here.
6cm
6.4 cm 5cm
What numbers are to be used in finding the area of the triangle?
What is the formula in finding the area?
Solution:
A=1/2 x (bxh)
A=1/2 x (6cm x 5cm)
A=1/2 x30cm2
A=15 sq. cm or 15 cm2
How about if the unknown is the length of the base? How will you solve that?
Solution for finding the base of the triangle:

3. Any whole numbers will have an automatically denominator of 1.
The formula in finding the length of the base is:
A=20m2
h=4m
Let us solve for the base of the triangle:
B=2A/h
=2(20m2
)/4m
=40m2
/4m
=10m
The base of the triangle is 10m.
Another example:
A=45m2
H=5m
Who will solve the base of the triangle on the board?
How about if the height is unknown? What is the formula?
H=2A/b
For example:
A=16cm2
B=4cm
Who will solve for the height of the triangle?
2. Post Activity
Solve the following what being asked:
a)
5cm
7cm
b)
4cm
6cm
c)
8m
12m
B=2A/h

4. 3. Generalization
What is the formula in finding the area of the triangle?
How will you derive the formula of the area of a triangle?
IV. Evaluation
1. Solve the area of triangle.
a.
5m
4m
b.
4m
10m
2. Find the base of a triangle.
A=52cm2
H=8cm
B=?
3. Find the height of a triangle.
A=49cm2
B=7cm
H=?
V. Assignment
Give the formula for the area of the triangle. Write the equation.
a.
10cm
15cm
b. B=30cm
c. H=12cm
_________________
Emilyn R. Ragasa
BEEd-III