The general equation of a circle is: x? +y？ +Dx+Ey+F=0(D？ +E？ -4F & gt； 0), where the center coordinate is (-D/2, -E/2).

Sector arc length L= central angle (radian system) ×R= nπR/ 180(θ is central angle) (r is sector radius).

Sector area S=nπ R? /360=LR/2(L is the arc length of the sector)

Radius of cone bottom surface r=nR/360(r is the radius of bottom surface) (N is the central angle)

Extended data:

A straight line and a circle have nothing in common, which is called separation. AB is separated from circle O, d>r. A straight line and a circle have two points in common, which are called intersections. This straight line is called the secant of a circle. AB intersects with o and d

A straight line and a circle have only one common point, which is called tangency. This straight line is called the tangent of the circle, and this common point is called the tangent point. The line between the center of the circle and the tangent point is perpendicular to the tangent line. AB is tangent to ⊙O, and d = r. (d is the distance from the center of the circle to the straight line)