Circle, center of circle, diameter, radius, Draw circle,
1.1. About circle
Comment : In a circle
- The center O is the midpoint of the diameter AB.
- The length of the diameter is twice the length of the radius.
1.2. Draw a circle
Use a compass to draw a circle with a radius of 2cm.
1.3. Solve the textbook exercises page 111
Lesson 1: Name the radius and diameter of each circle:
- Radius: The line segment connecting the center to a point on the circle.
- Diameter: The line segment passing through the center, connecting two points lying on the circle.
a) Radius: OM, ON, OP, OQ.
Diameter: MN, PQ.
b) Radius: OA, OB.
Lesson 2: Please draw a circle with
a) Center O, radius 2cm
b) Center I, radius 3cm.
Use a compass to draw a circle:
- Open the compass a distance equal to the radius of the circle to be drawn.
- Mark a fixed point on the notebook, name it and call it the center.
- Place one fixed leg of the compass with the center, keep it fixed and rotate the other leg once, from which you get a circle with arbitrary center and radius.
a) Draw radius OM, diameter CD of the following circle:
b) Which sentence is true and which is false?
– The length of the line segment OC is longer than the length of the line segment OD.
– The length of line segment OC is shorter than the length of line segment OM.
– The length of line segment OC is half the length of line segment CD.
- Mark any point M on the circle, connect O to M. Through O draw a line, cut the circle at two points, name it C and D.
- Using knowledge: In a circle, the radii are of equal length and the length of the diameter is twice the length of the radius.
– The length of the line segment OC is longer than the length of the line segment OD (False, because OC and OD are both radii of a circle, they have the same length)
– Length of line segment OC is shorter than length of line segment OM (False)
– The length of the line segment OC is half of the length of the line segment CD (Correct because in a circle the radius length is half the length of the diameter).
1.4. Textbook exercise solution page 112
Lesson 1: Draw a picture according to the following steps
Step 1: Draw a circle with center O and radius OA.
Step 2: Draw a circle decoration (center A, radius AC; center B, radius BC).
Step 3: Draw a circle decoration (center C, radius CA; center D, radius DA).
Lesson 2: Color the picture drawn in lesson 1