Radius is one of the important properties of a circle, which is used to calculate its area and perimeter. For example, the formula for the area of a circle is πr? , where π represents the ratio of the circumference to the diameter of the circle and r represents the radius of the circle. Radius can also be used to calculate the volume and surface area of a ball, because the radius of a ball is similar to that of a circle.
In trigonometric functions, r often represents the polar diameter, that is, the distance from the coordinate origin to the (x, y) point, which is used to calculate the angle in the polar coordinate system. In addition, in statistics and data analysis, R can also represent correlation coefficient to measure the strength and direction of the relationship between two variables.