arc length formula: n is the central angle of the circle, r is the radius, and α is the central angle in radians. l=nπr÷180 or l=n/180·πr or l=|α|r

in a circle with radius r, because the arc length subtended by a central angle of 360° is equal to the circumference c=2πr, the arc length subtended by a central angle of n° is l=n°πr÷180°.

in the radian system, if the central angle subtended by the arc is θ, then there is the formula l=rθ. the sector area formula s=lr/2, and the corresponding sector area calculation formula s=rrθ/2.

in a circle, the line segment connecting the center of the circle to any point on the circle is called the radius of the circle. usually represented by the letter r.

the vertex of the central angle is at the center of the circle, and the angle where both sides of the angle intersect the circumference is called the central angle. the value range of the central angle ∠aob is 0°＜∠aob＜360°