Question

Using ruler and compasses only, draw an equilateral triangle of side 4.5 cm and draw its circumscribed circle. Measure the radius of the circle.  

Answer 1

 
Steps of construction:

1. Draw a line segment BC = 4.5 cm.
2. With centers B and C, draw two arcs of radius 4.5 cm which intersect each other at A.
3. Join AC and AB.
4. Draw perpendicular bisectors of AC and BC intersecting each other at O.
5.  With centre O and radius OA or OB or OC draw a circle which will pass through A, B and C.
   This is the required circumcircle of triangle ABC.
   On measuring the radius OA = 2.6 cm.