Construct an equilateral triangle $ABC$ with side $4 \; cm$. Draw a circle touching the sides of the triangle.
Construct an equilateral triangle with each side equal to $4 \; cm$.
Draw perpendicular bisectors $PQ$ and $RS$ of sides $AB$ and $BC$ respectively.
The perpendicular bisectors intersect at point $O$.
With $O$ as center and $OA$ as radius, draw a circle which passes through all the vertices of the equilateral triangle $ABC$.