### Theory:

Familiarize yourself with the mathematics tool - the Compass.

Compass can look different, but all whips have two legs - a sharp-pointed pin and a pencil.

Compass can be used to draw a circle.

If you mark a small mark or dot on a piece of paper and place the sharp crank leg at that point, you can draw a circle. The dot is called the center of the circle, and we usually denote by the capital letter \(O\).

The segment joining center \(O\) of a circle to a point on the circle (point A in the drawing) is called the radius.

The figure shows that the radius of the circle \(OA\) is \(5\)\(cm\) (Figure: 1).

Compass is needed - with the feet of the cruiser measured to the desired distance to draw a circle with a given radius.

**Figure: 1**

- The coloured part inside is the area of a circle. (Figure: 2).

**Figure: 2**

The segment passing through the center of the circle and joining the two points of the circumference is called the diameter.

- The diameter is \(EF\) (Figure: 3).

**Figure: 3**

- The segments \(AO, BO, CO, EO, FO\) are the radii of the circumference (Figure: 3).

The radii of the circle are equal in length.

\(AO = BO = CO = EO = FO\)

\(AO = BO = CO = EO = FO\)

The diameter of the circle is \(2\) times longer than the radius.

If the radius of the circle is \(5\)\(cm\), then the diameter is \(2·5 = 10\) (\(cm\)).