Copying a Triangle
Geometry construction using a compass and straightedge
Step-by-step Instructions Printer friendly version
After doing this Your work should look like this
Start with the triangle ABC which we will copy. Geometry construction with compass and straightedge or ruler or ruler
1.  Mark a point P that will be one vertex of the new triangle Geometry construction with compass and straightedge or ruler or ruler
2.  Set the compass width to the length of one side of the original triangle ABC. In this example we use AC. Geometry construction with compass and straightedge or ruler or ruler
3.  With the compass point on P, make an arc near where the next vertex of the triangle will be. Geometry construction with compass and straightedge or ruler or ruler
4.  Mark a point R on the arc. This will become the next vertex of the new triangle. PR is equal in length to AC Geometry construction with compass and straightedge or ruler or ruler
5.  Use the compass to measure the length of the side AB in the original triangle. Geometry construction with compass and straightedge or ruler or ruler

6.   Place the compass point on P and make an arc in the vicinity of where the third vertex of the triangle will be.

All points along this arc are the distance AB from P, but we do not yet know exactly where on this arc the the vertex is.

Geometry construction with compass and straightedge or ruler or ruler
7.  Use the compass to measure the length of the side BC in the original triangle Geometry construction with compass and straightedge or ruler or ruler
8.  From point R, draw an arc crossing the first. where these intersect is the vertex Q of the triangle Geometry construction with compass and straightedge or ruler or ruler
9.  Finally, draw the three sides of the new triangle PQ ,PR, and QR. Geometry construction with compass and straightedge or ruler or ruler
10.  Done. The blue triangle PQR is congruent to the triangle ABC. Geometry construction with compass and straightedge or ruler or ruler
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.

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Non-Euclidean constructions