1995 There is no circle in the sixth grade of primary school. At that time, the study of circular area was carried out in junior high school, so the sixth grade of primary school was not offered.

Formula related to circle:

1, circular area: S=πr? ，S=π(d/2)？ . (d is the diameter and r is the radius).

2. area of semicircle: s semicircle = (π r 2)/2. (r is the radius).

3. Ring area: s great circle -S small circle = π (r 2-r 2) (r is the radius of great circle and r is the radius of small circle).

4. Circumference: C=2πr or c = π d..(d is the diameter and r is the radius).

5. The circumference of a semicircle: d+(πd)/2 or d+π r (d is the diameter and r is the radius).

6. The area of the circle where the sector is located is divided by 360 and multiplied by the angle n of the central angle of the sector, as shown below:

S=n/360×πr？ .

S=πr？ ×L/2πr=Lr/2(L is arc length and r is sector radius).