Circle, circle đường
1.1. Knowledge to remember
The pointer of the compass traces a circle on the paper
– Connect the center O to a point A on the circle. The line segment OA is the radius of an equal circle: OA = OB = OC.
– The line segment MN connecting two points M, N of the circle and passing through the center O is the diameter of the circle.
In a circle, the diameter is 2 times the radius.
1.2. Solve textbook exercises on pages 96 and 97
Lesson 1 Textbook page 96:
Draw a circle with:
a) 3cm radius; b) Diameter 5cm.
in question b), the radius of the circle is:
5: 2 = 2.5 (cm)
– Mark a point, such as O (or I), as the center.
– Open the compass so that the tip of the needle is about 3cm (or 2.5cm) from the tip of the lead.
– Put the needle in the O point, press the lead tip close to the paper face to rotate exactly one revolution. We get a circle with center O (or I) with radius 3cm (or 2.5cm).
a) 3cm radius:
b) Diameter 5cm:
Lesson 2 Textbook page 96:
Let the line segment AB = 4cm. Draw a circle with center A and center B both with radius 2cm.
Using a compass to draw a picture into a notebook according to the instructions above, we have the following drawing
Lesson 3 Textbook page 97:
– Draw a circle with center O and radius 4 times the side of the square.
Determine the diameter AB of the circle.
– Draw a semicircle with diameter AO (OB) towards the bottom (or top).