Construct an equilateral triangle whose perimeter is 15 cm?
steps of construction:
1. let us draw a straight line PQ=15 cm.
2. at P draw an angle RPQ=60 deg, at Q draw an angle SQP=60 deg.
3. now we will draw the angle bisectors of ∠RPQ and ∠SQP. let it intersect at point A.
4. draw the perpendicular bisector of PA and QA. let it intersect PQ at B and C respectively.
5. join AB and AC.
thus ABC is the required triangle.