Steps for construction:

i) Draw a line segment BC = 4.5 cm

ii) With centres B and C, draw two arcs of radius 4.5 cm which intersect each other at A.

iii) And join AC and AB.

iv) Draw the perpendicular bisectors of AC and BC which intersect each other at O.

v) With centre O, and radius OA or OB or OC draw a circle which will pass through A, B and C.

Then, this is the required circumcircle of triangle ABC.

Therefore, the radius, we get OA = 2.6 cm