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Properties of Circles

Properties of Circles

A circle is a line drawn at a fixed distance from a point. The point is called the centre, and the line that is drawn a fixed distance from it is called the circumference.

The distance from the centre to the circumference is the radius.

A line joining one part of the circumference to another part of the circumference is known as a chord. A chord that goes through the centre of a circle is a diameter, and has twice the length of the radius.

Properties of the parts of a circle

Example 1

A circle has a radius of 8cm. What is the longest chord that can be drawn on the circle?

The longest chord must go through the centre of the circle. This is the diameter; the diameter is twice the value of the radius. 2 x 8 = 16cm.

Answer: 16cm

Example 2

A line is drawn from the centre of a circle to its circumference. The diameter of the circle is 6cm. What is the length of the line?

The line from the centre of a circle to its circumference is the radius, and the radius is half the diameter. 6 รท 2 = 3cm.

Answer: 3cm