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.

*Solution guide:*

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.

*Solution guide:*

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:

Pattern drawing:

*Solution guide:*

– 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).

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