The chapter of circle in sixth grade mathematics is a difficult point for sixth grade students. In addition to the calculation of circular correlation, the key difficulty lies in the calculation of perimeter and area of combined graphics. This part not only examines everyone's ability to use knowledge, but also examines how to use some special skills and methods to solve problems in the learning process, which is exactly what everyone lacks in learning.

First of all, the names of the parts of the circle:

1, the center of the circle-the point on the center of the circle is called the center of the circle, which is generally represented by the letter O.

2. Radius-The line segment connecting the center of the circle with any point on the circle is called the radius, which is generally represented by the letter R..

3. Diameter-The line segment passing through the center of the circle and with both ends on the circle is called diameter, which is generally represented by the letter D. ..

4. A circle has only one center, countless radii and countless diameters.

Second, the characteristics of the circle:

1, the center of the circle determines the position of the circle, and the radius (or diameter) determines the size of the circle.

2. The diameter is the longest line segment in a circle.

3. The straight line with diameter is the symmetry axis of the circle.

Third, draw a circle with compasses:

1. Separate the two feet of the compass and set the distance between the two feet as the radius.

2. Fix the foot on a point with the needle tip as the center of the circle.

3. Rotate your feet once with pencil lead and draw a circle.

4. Many beautiful patterns can be designed as circles.

Fourth, the circumference of the circle:

1, definition of circumference: the length of a curve around a circle is called circumference, which is generally represented by the letter C.

2. Pi: The ratio of the circumference to the diameter of a circle is a definite value. This fixed value is pi, which is expressed by the letter π. π is generally calculated to be 3. 14.

3. The formula for calculating the circumference of a circle: C=2πr or c = π d.

4. Perimeter of a semi-circle: The perimeter of a semi-circle is half of the circumference plus 2 radii or 1 diameter.

Five, the area of the circle:

1, the definition of the area of a circle: the size of the plane occupied by a circle is called the area of a circle, which is generally represented by the letter S.

Six, two typical problems:

1. Draw the largest circle in a square-the side length of a square is the diameter of the largest circle.

2. Draw the largest square in the circle-the diagonal length of this square is the diameter of the circle.

Seven, fan:

1, arc: The part between any two points on a circle is called an arc. An arc is a part of a circle.

2. Sector: The figure enclosed by an arc and two radii passing through both ends of the arc is called a sector.

3. Central angle: It consists of two radii, and the angle with the center of the circle as the vertex is called the central angle.

4. In the same circle or equal circle, the size of the sector is related to the size of the central angle of the sector. The bigger the central angle, the bigger the sector.