The two important properties on circle are stated below:

**1. The ratio of the circumference to the diameter of any circle is constant and the value of this constant is denoted by the Greek letter π.**

Therefore, the circumference of any circle/diameter of that circle = constant = π

or, the circumference of any circle = π × diameter of that circle.

If r be the radius of the circle then its diameter is 2r.

Therefore, the circumference of the circle = π ∙ 2r = 2πr.

The constant quantity π is an incommensurable number i.e., it cannot be expressed as the ratio of two positive integers. An approximate value or π is 27/7; a more accurate value of π is 355/133 or, 3.14159 (correct to five places of decimals).

**2. Angles at the center of a circle are proportional to the lengths of the arcs which subtend those angles.**

The above two important properties on circle will help us to prove that a radian is a constant angle.

**Click Here** to know how to prove that “**a radian is a constant angle**”.

**●** **Measurement of Angles**

**Sign of Angles****Trigonometric Angles****Measure of Angles in Trigonometry****Systems of Measuring Angles****Important Properties on Circle****S is Equal to R Theta****Sexagesimal, Centesimal and Circular Systems****Convert the Systems of Measuring Angles****Convert Circular Measure****Convert into Radian****Problems Based on Systems of Measuring Angles****Length of an Arc****Problems based on S R Theta Formula**

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