Page 141 - NUMINO TG_6A
P. 141
09Unit Transforming It into a Parallelogram
jOb ective Find the area of a circle by using the area of a parallelogram.
1. Textbook Instructions 09 Transforming It into a Parallelogram
Pi, used to find the circumference of a circle, is The radius of the circle is 5 cm.
also used to find the area of a circle. Students Estimate its area.
will understand how to find the area of a circle
and learn the formula. 1 cm
1 cm
First, have the students look at the circle
drawn on the grid. Color the square if more than half is in the circle.
There is a circle drawn on the grid. How Count the number of colored squares. How many squares are colored?
can you find the area of the circle? Count
the number of squares. 80 squares
Color a square if more than half of it lies in
the circle. How many squares are colored? What is the area of each small square? Each small square is 1 cm2.
80 squares. Estimate the area of the circle. About 80 cm2.
What is the area of 1 square? The area of 1
square is 1 cm2.
What is the area of the colored part? 80
cm2.
Is the area of the colored squares the same
as the area of the circle? No, they are not the
same.
What is the estimated area of the circle?
About 80 cm2.
74
2. Build Understanding
Area of Circles
Estimate the area of a circle. 4 cm
Have the students use a compass to draw a circle with a 2 cm radius.
Have them draw an interior and exterior square (shown on the right).
Find the length of the larger square, and calculate the area. 2.83 cm
S: 4 cm, A: 4 4 16 (cm2)
Find the length of the smaller square, and calculate the area.
S: 2.83 cm, A: 2.83 2.83 8 (cm2)
The area of the circle is greater than the area of the smaller square, but smaller than the area of the larger square, so
it is between 8 cm2 and 16 cm2.
This method does not show the method to accurately calculate the area of the circle.
124 NUMINO Teacher s Guide
jOb ective Find the area of a circle by using the area of a parallelogram.
1. Textbook Instructions 09 Transforming It into a Parallelogram
Pi, used to find the circumference of a circle, is The radius of the circle is 5 cm.
also used to find the area of a circle. Students Estimate its area.
will understand how to find the area of a circle
and learn the formula. 1 cm
1 cm
First, have the students look at the circle
drawn on the grid. Color the square if more than half is in the circle.
There is a circle drawn on the grid. How Count the number of colored squares. How many squares are colored?
can you find the area of the circle? Count
the number of squares. 80 squares
Color a square if more than half of it lies in
the circle. How many squares are colored? What is the area of each small square? Each small square is 1 cm2.
80 squares. Estimate the area of the circle. About 80 cm2.
What is the area of 1 square? The area of 1
square is 1 cm2.
What is the area of the colored part? 80
cm2.
Is the area of the colored squares the same
as the area of the circle? No, they are not the
same.
What is the estimated area of the circle?
About 80 cm2.
74
2. Build Understanding
Area of Circles
Estimate the area of a circle. 4 cm
Have the students use a compass to draw a circle with a 2 cm radius.
Have them draw an interior and exterior square (shown on the right).
Find the length of the larger square, and calculate the area. 2.83 cm
S: 4 cm, A: 4 4 16 (cm2)
Find the length of the smaller square, and calculate the area.
S: 2.83 cm, A: 2.83 2.83 8 (cm2)
The area of the circle is greater than the area of the smaller square, but smaller than the area of the larger square, so
it is between 8 cm2 and 16 cm2.
This method does not show the method to accurately calculate the area of the circle.
124 NUMINO Teacher s Guide
