Method 1: Calculate the circle radius with known diameter;

The calculation formula is: D = 2r. Where "d" stands for diameter and "r" stands for radius. The formula can be converted into r = D/2.

Method 2: Find the radius from the known perimeter;

The formula of perimeter is C= 2πr, where "r" stands for radius and π is pi (3. 14 159 ...). The formula for converting into radius is r = C/2π.

Method 3: Calculate the radius of the known area;

The area of a circle is A = πr2 (square here). You can get the transformation formula, r = √A/π ("the radius r is equal to the circle area divided by π, and then take the square of the value").

Method 4: Know the coordinates of three points on the circle and find the radius of the circle.

Three points can define a circle. Any three points on the coordinate plane can form a circle whose circumference passes through three points. The center of a circle may be outside or inside a triangle formed by three points, depending on the positions of the three points. The center of the circle is also called the "outer center" of the triangle, and the radius is also called the "circumscribed circle radius". If the coordinates (x, y) of three points are known, the radius of the circumscribed circle can be found.

Radius:

In mathematical geometry, it refers to half the distance between the longest two points on a circle. It is called radius, and the diameter is twice the radius, which is equivalent to the radius multiplied by 2 equals the diameter.

Related definitions:

In a circle, the line segment connecting the center of the circle and any point on the circle is called the radius of the circle. Usually represented by the letter R.

In a sphere, the line segment connecting the center of the sphere and any point on the sphere is called the radius of the sphere.

The radius of the circumscribed circle where the regular polygon is located is called the radius of the inscribed circle of the regular polygon.

Related calculation method:

(1) perimeter =2πr(2* pi * radius)

(2) Circular area =πr? (pi * radius? )

(3) Diameter =2r (the diameter is twice the radius)