Lesson Notes By Weeks and Term - Junior Secondary 2
Area of plane figures
Area of plane figures
TERM – 2ND TERM
WEEK FOUR & FIVE
Class: Junior Secondary School 2
Age: 13 years
Duration: 40 minutes of 5 periods each
Date:
Subject: BASIC TECHNOLOGY
Topic: AREA OF PLANE FIGURES
SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to
INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,
demonstration, videos from source
INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures, mathematical sets, drawing instruments.
INSTRUCTIONAL PROCEDURES
PERIOD 1-2
|
PRESENTATION |
TEACHER’S ACTIVITY |
STUDENT’S ACTIVITY |
|
STEP 1 INTRODUCTION |
The teacher explains the meaning of enlargement and reduction in plane figures. |
Students pay attention |
|
STEP 2 EXPLANATION |
Teacher enlarge/Reduce plane figures |
Students pay attention and participate |
|
STEP 3 DEMONSTRATION |
Teacher explains how to determine areas of regular and irregular plane figures. |
Students pay attention and participate |
|
STEP 4 NOTE TAKING |
The teacher writes a summarized note on the board |
The students copy the note in their books |
NOTE
AREA OF PLANE FIGURES
Enlargement/Reduction of Plane Figures
Enlargement is the transformation of an object that has the same shape, but increases in size of the object.
Reduction is a transformation of an object that has the same shape, but decreases in size of the object.
In both enlargement and reduction, the angles of the shapes remain the same, only the sides of the shape enlarge (bigger) or reduce (smaller).
Enlargement and reduction are an example of similar shapes (shapes with the same shape but different sizes).
The amount of which the object is enlarged or reduced is called the factor of enlargement or the factor of reduction. This can also be called the scale Factor
i.e, Scale Factor = length of the enlargement
Corresponding length
For example: An object is given to be enlarge with a ratio of 1:2
Procedure
1. Draw an oblique line from a suitable corner. For instance, point A
2. Sum up the total of the numbers in the given ratio 1:2
i.e 1 + 2 = 3
Mark from point A mark 3 equal divisions on the oblique line
3. Draw a straight line from point 1 to point B at the end of line AB
4. Project line AB more to the right. Now, draw a line parallel to line 1B from point 3 to intersect with the projected line at C.
5. From point A, project lines to pass through each corner of the object.
6. From point C, draw main lines parallel to each side of the object.
An object is given to be reduce an object to a ratio of 5 : 3
Procedure
1. Draw an oblique line from a suitable corner. For instance point A
2. The highest number in the given ratio 5 : 3 is 5. From point A mark 5 equal divisions on the oblique line.
3. Draw a straight line from point 5 to point B at the end of the line AB
4. Draw a line parallel to line 5B, from point 3 to intersect with line AB at C
5. From point A project lines to pass through every corner of the object.
6. From point C, draw main lines parallel to each sides of the object
Determination of Areas of Regular and Irregular Figures
To find the Area of Irregular Shapes, first, we need to divide the Irregular Shape into Regular Shapes that you can recognize such as triangles, rectangles, circles, Squares and so forth.Then, find the Area of these individual Shapes and add them to get an Area of Irregular Shapes.
Example. Find the Area of the given Shape?
Solution:
The figure above has three Regular Shapes.
Start dividing from the top, it has a triangle, a rectangle, and a trapezoid.
We will find the Area for each of those three Shapes and add the results to get the final Area of a figure.
Triangle Area of triangle = (base × height)/2= (3 × 4)/2= 12/2= 6
Rectangle Area of rectangle = length × width= 4 × 10= 40
Trapezoid Area of trapezoid = ((b1 + b2) × h)/2= ((3 + 5) × 2)/2= (8) × 2/2= 16/2= 8
Thus Area of the given Shape = 6 + 40 + 8 = 54.
EVALUATION: 1. What is enlargement and reduction.
CLASSWORK: As in evaluation
CONCLUSION: The teacher commends the students positively