A Semi-detailed Lesson Plan in Mathematics
I.
OBJECTIVES
At the end of the discussion, the
students are expected to:
1.
Identify
the parts of a triangle.
2.
Compute
the area of a triangle given with the base and the height.
3.
Compute
the area of a triangle given with the lengths of the sides using Microsoft
Math.
II.
CONTENT and
MATERIALS
a. Subject Matter: Area of a Triangle
b. Materials: activity sheets and
computer(s)
c. References:Microsoft ® Encarta ® 2009. ©
1993-2008 Microsoft Corporation.
III.
PROCEDURES
A.
Preparatory
Activities
1.
Review
Review
the definition of literal equation and provide review exercises.
B.
Developmental
Activities
1.
Motivation
Let the students identify the different
types of triangle base on figures:
a. right triangle
b. acute triangle
c. obtuse triangle
Let the students identify the different
types of triangle base on the lengths of the sides and some measures of the
angles using the Microsoft Math.
a. a=32; b=24; angle C = 62 (Scalene triangle and Acute triangle)
b. c=12; a=35; angle B = 58 (Scalene triangle and Obtuse triangle)
c. angle A = 38; angle C = 52; b=12 (Scalene triangle and Right triangle)
2.
Presentation
Present
a word puzzle and let the students arrange the letters to form four words
pertaining to the new lesson of the day which will be “AREA OF A TRIANGLE”.
3.
Discussion
Triangles
with different length sides may have the same area. The area of a triangle is
dependent only on the length of its base and on its perpendicular height.
How can we
calculate the area of a triangle from this information?
Calculating the area of a triangle
I. Base and Height
We can choose any
side of a triangle as the base. For convenience, the same word (base) is used
to denote the length of this side. Once a base has been chosen there is only
one perpendicular height relative to this base; this is the straight line
perpendicular to the base, passing through the opposite apex.
A. Formula
Let A be
the area of a triangle of base b and perpendicular height h;
h
b
Thus,
To apply this
formula A, b, and h must be expressed in corresponding
units; for example: b and h in cm and A in cm2.
B. Example
Solve the area of
this triangle,
 |
8
cm
10
cm
Given: h = 8 cm; b = 10 cm
Formula:
Solution:
II.
Lengths of the Sides
A
triangle has three sides with either equal or unequal lengths. These measures
can be used to find the area of a triangle but with finding first its perimeter.
We usually denote the sides of the triangle with the lower case letter of the
corresponding opposite angles.
A.
Formula
Let
A be the area of a triangle of sides a,
b, c, and half of its perimeter s;
B
c a
A C
B
Thus,
wherea, b, and c are
the lengths of the sides of the triangle and s is one-half of its
perimeter.
B.
Example
1.
Find the area of this triangle,
B
14 cm 6 cm
A C
10 cm
Given: a = 6 cm; b = 10 cm; c = 14
cm
P = 30 cm; s = 15 cm
Formula:
Solution:
2. Find the area of the triangle with sides of
lengths 12 cm, 12 cm, and 20 cm using the Microsoft Math.
Formula:
Solution:
4.
Application
Let
the student solve the following using Microsoft Math:
1. Find the area of the triangle with sides of
lengths 21 cm, 41 cm, and 34 cm.
2. Find the area of the triangle with sides of
lengths 23.5 in, 10.5 in, and 32 in.
3. Find the area of the triangle with sides of
lengths 14 m, 19 m, and 11 m.
5.
Generalization
Finding
the area of a triangle can be based to what are given. If the base and the
height are known, the formula is
used where b is the base and h is the height. Moreover, if the lengths of the
sides are given, the formula is used.
is
used where b is the base and h is the height. Moreover, if the lengths of the
sides are given, the formula is used.
IV. EVALUATION
Group the students into three. Each group
shall be given a set of problems with five questions per set; all will require
finding the area of the triangle using Microsoft Math. Every member of the
group shall perform one task on the computer that will be placed in front, that
is, to find the area of a triangle given only with the lengths of the sides.
After a member had done getting the area, s/he will run back to their line and
give the answer to one of their members whose task is only to write all the
answers and then another member will work in the computer to answer the next
problem and so on. After all of the members who are tasked to answer the
problems are finished, the total number of problems answered will be recorded,
thus, after all of the groups had done the activity, the group with the highest
number of correct answers shall earn the highest points
and the next two respective groups will be rewarded with corresponding points
as well.
V. ASSIGNMENT
Answer the problems in
page 213-214 in your book. Use the Microsoft Math and encode your answers in
the Microsoft Word. Send your work through this e-mail address
cherryanni@yahoo.com
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