Copying a Triangle
Geometry construction using a compass and straightedge

Given a triangle, this page shows how to construct another triangle that is congruent to it using a compass and straightedge or ruler.

Printable step-by-step instructions

The above animation is available as a printable step-by-step instruction sheet, which can be used for making handouts or when a computer is not available.

Proof

The image below is the final drawing above.

  Argument Reason
1 PR is congruent to (same length as) AC PR drawn with compass width set from AC
2 RQ is congruent to (same length as) CB RQ drawn with compass width set from CB
3 PQ is congruent to (same length as) AB PQ drawn with compass width set from AB
4 Triangles ABC, PQR are congruent (same shape and size) Congruence rule SSS - three sides congruent
5 Triangle PRQ is an exact copy of triangle ABC From (4)

  - Q.E.D

Try it yourself

Click here for a printable worksheet containing two triangle copying problems. When you get to the page, use the browser print command to print as many as you wish. The printed output is not copyright.

Constructions pages on this site

Lines

Angles

Triangles

Right triangles

Triangle Centers

Circles, Arcs and Ellipses

Polygons

Non-Euclidean constructions

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