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Copying a Triangle
Click here for a printable triangle copying worksheet
How to construct a a triangle that is congruent with a given
triangle, using only a
compass and straightedge.
We start with a given triangle ABC, and the result is a new triangle PQR which is congruent to it.
Instructions Click on 'Next' to go through the construction one step at a time, or click on 'Run' to let it run without stopping.
(If there is no image below, see support page.)
Step-by-step Instructions
| Step 1 |
Mark a point P that will be one vertex of the new triangle |
| Step 2 |
Set the compass width to the length of one side of the original triangle ABC. In this example we use AC. |
| Step 3 |
With the compass point on P, make an arc near the next vertex of the triangle. |
| Step 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 |
| Step 5 |
Use the compass to measure the length of the side AB in the original triangle. |
| Step 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 quite know exactly where the the vertex is. |
| Step 7 |
Use the compass to measure the length of the side BC in the original triangle |
| Step 8 |
From point R, draw an arc crossing the first. where these intersect is the vertex Q of the triangle |
| Step 9 |
Finally, draw the three sides of the new triangle PQ ,PR, and QR. |
| Step 10 |
Done. The blue triangle PQR is congruent to the triangle ABC. |
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.
Other constructions
Lines
Angles
Triangles
Triangle Centers
Circles, Arcs and Ellipses
Non-Euclidean constructions
(C) 2007 Copyright John Page
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