This lesson plan outlines a mathematics class on Heron's formula for calculating the area of a triangle. The teacher will begin with an introductory activity to recall what students know about finding the area of polygons and triangles. Through an example, the teacher will demonstrate calculating the area of a triangle without Heron's formula. The content analysis defines Heron's formula and its terms. Learning outcomes include understanding and applying Heron's formula through examples. Students will work in groups and individually, with guidance from the teacher, to understand and use Heron's formula to find the area of triangles.

1. LESSON PLAN-23
Name of the teacher : Nisha Rajan
Subject : Mathematics
Unit : Area
Subunit : Heron’s formula
Name of the school : St Stephen’s
HSS, PTPM
Standard : IX
Strength : 34/38
Date : 23/08/2015
Time : 40 minutes
CURRICULAR STATEMENT
To understand about the Heron’s formula and its importance in Mathematics
through observation, discussion and analyzing the prepaid notes of the pupil.
CONTENT ANALYSIS
New Terms : Heron’s formula
Facts : Area of triangle = √𝑠(𝑠 − 𝑎)(𝑠 − 𝑏)(𝑠 − 𝑐)
Where a , b and c are sides of triangle and s =
𝑎+𝑏+𝑐
2
.
Concept : Concept of Heron’s formula.
Process : Process of understanding Heron’s formula.
LEARNING OUTCOMES
The pupil will be able to :-
1. Recall the terms, triangle and area of triangle.
2. Recognize Heron’s formula.
3. Identify the concept of Heron’s formula.
4. Give illustration for Heron’s formula.
5. Through familiar examples an unfamiliar is made clear.
6. Ask questions to know more about Heron’s.

2. PRE-REQUISITES
Students have knowledge on triangle and its area.
TEACHING LEARNING RESOURCES
Usual classroom aids and charts.
LEARNING STRATERGIES
Group discussion , individual work , observation and explanation by the teacher.
Classroom interaction procedure Expected pupil responses
INTRODUCTION
ACTIVITY 1
1. How do we find the area of polygon?
2. How do we compute the area of
triangle?
By asking these questions teacher
leads the students to the topic.
PRESENTATION
ACTIVITY 2
Teacher give a problem of
finding the area of triangle with sides
are 4m, 5m and 7m. Teacher explains
the method of finding the area
through an example
 Calculate the perimeter of the
triangle
𝑃 = 4 + 5 + 7 = 16𝑚
 Take its half
16
2
= 8𝑚
 Subtract the length of each side
from this.
Most of pupil answer correctly
Pupil says that area of triangle
A = 1
2
bh
Pupil understand the method and
write down.

3. Classroom interaction procedure Expected pupil responses
8 − 4 = 4𝑚
8 − 5 = 3𝑚
8 − 7 = 1𝑚
 Multiplying together, half the
perimeter and the numbers got by
subtracting the length of sides
8 × 4 × 3 × 1 = 96
Take it square root
√96 =√16 × 6 =4√6 𝑚2
≈ 9.8 𝑚2
 Let a,b,c be the length of sides of a
triangle and let
𝐴 = √𝑠(𝑠 − 𝑎)(𝑠 − 𝑏)(𝑠 − 𝑐)
It is called Heron’s formula.
Teacher shows chart contains
Heron’s formula.
ACTIVITY 3
Teacher gives a problem can you
compute the area of a triangle of
sides 10, 12 and 15 cm?
Teacher asks the pupils that ,
What is to be find out?
What is given?
What is the formula for finding the
area?
Pupils listen
Pupil read the chart.
Pupil answers that we have to find
the area of triangle.
The sides of triangle are given,
𝐴 = √𝑠(𝑠 − 𝑎)(𝑠 − 𝑏)(𝑠 − 𝑐)

4. Classroom interaction procedure Expected pupil responses
𝑎 = 10 , 𝑏 = 12 , 𝑐 = 15
𝑠 =
𝑎+𝑏+𝑐
2
=
37
2
Area = √𝑠(𝑠 − 𝑎)(𝑠 − 𝑏)(𝑠 − 𝑐)
=
√
37
2
(
37
2
− 10)(
37
2
− 12)(
37
2
− 15)
= √
37
2
×
17
2
×
13
2
×
7
2
=
239.24
4
= 59.81 𝑐𝑚
CLOSURE
ACTIVITY 4
Teacher concludes the class by
saying about Heron’s formula.
REVIEW
ACTIVITY 5
Teacher asks questions about
Heron’s formula.
FOLLOW UP ACTIVITY
1. Find the area of triangle of sides
6m, 8m and 10m.
2. Find the area of triangle of sides
20cm,29cm and 21cm.
Pupil answer correctly.