Draw a circle using a compass and mark:

(a) Centre as O (b) Radius as OA (c) Diameter as AB

Steps of construction:

(i) Mark a point O as the centre.

(ii) Open the compass to a suitable radius. Place the compass needle at O and draw a complete circle.

(iii) Mark any point A on the circle and join OA. Then OA is a radius.

(iv) Extend AO to meet the circle again at B and join AB. Then AB is a diameter passing through the centre O.