1, the circumference of the circle is: C=πd or C=2πr (where? D is the diameter of the circle and r is the radius of the circle).

2. Formula of circular area: S=πr? Or S=π×(d/2)? . (π stands for π(3. 14 15927 ...), r stands for radius and d stands for diameter).

Extended data:

1, the circumference of a circle means that the n-polygon is inscribed in the circle, the side length is set to an, and the circumference of a regular polygon is n×an. When n increases, the circumference of a regular polygon approaches the circumference of the circle, that is, n approaches infinity, and C=n×an.

2. Pi: Mathematician Liu Hui uses the secant method, that is, the circumference of a circle inscribed with a regular polygon and circumscribed with a regular polygon approaches the circumference of a circle, and the circle approaches 192 sides, and the pi is about 3. 14.

3. Sector area:

In a circle with radius r, the sector area corresponding to the central angle of 360 is the circle area S =πR2；; ; , so the sector area with the central angle of n:

S=(nπR2)÷360

There is another area formula for the sector.

S= 1/2lR (where l is arc length and r is radius)

Originally S=(nπR2)÷360.

According to the arc system. 2π=360 degrees. Because the unit of n is degrees, L is the corresponding arc length when the angle is n, that is, L = θ r = (n/180) π× r.

∴s=(n/ 180)π*r*π*r/2π= 1/2lr.

References:

Baidu encyclopedia-circumference

Baidu Encyclopedia-Area of Circle