Radius: The line segment connecting the center of the circle and any point on the circle is called the radius, which is represented by the letter "R".
Diameter: The line segment passing through the center of the circle with both ends on the circle is called diameter, which is represented by the letter "D".
2. The center of the circle determines the position of the circle, and the radius determines the size of the circle.
3. In the same circle, all radii are equal and all diameters are equal.
The same circle has countless radii and countless diameters.
The diameter of the same circle is twice the radius, and the radius is half the diameter. With the letter: d = 2rr = 2 (1) d.
4. The circumference of the circle: The length of the curve around the circle is called the circumference of the circle.
The circumference of a circle is always more than 3 times the diameter, and this ratio is a fixed number.
We call the ratio of the circumference to the diameter of a circle pi, which is expressed by the letter pi.
Pi is an infinite cyclic decimal. In the calculation, π≈3. 14 is taken.
The first person in the world to calculate pi was China mathematician Zu Chongzhi.
6. The circumference formula of a circle: C=πd or c = 2 π r.
7. Area of the circle: The size of the plane occupied by the circle is called the area of the circle.
8. Cut a circle into an approximate rectangle. The length of the cut rectangle is equivalent to half of the circumference, and the width is equivalent to the radius of the circle. Because the area of a rectangle = length× width, and the area of a circle =πr×r=πr2.
9. Formula of circular area: S=πr2 or S=π(d÷2)2 or S=π(C÷π÷2)2.
10. Draw the largest circle in a square, and the diameter of the circle is equal to the side length of the square. The ratio of the area of a circle to that of a square is π: 4. To draw the largest square in a circle, the length of the circle diameter is equal to the length of the diagonal of the square, and the area of the square = diagonal x diagonal ÷2= diameter x diameter ÷2.