How to copy an angle with compass and straightedge or ruler

Copying an Angle

Geometry construction using a compass and straightedge

- Printable problem worksheet
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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

After doing this	Your work should look like this
Start with a angle BAC that we will copy.
1. Using the straightedge, draw a reference line and place a point P near the left end.
2. Set the compass width to the distance AC, and without adjusting the compass, place it on P and mark an arc across the line. This establishes the point Q
3. With the compass on point A set its width to the the point B.
4. Without changing the compass width, place the compass point on the the point P and draw an arc above the line.
5. Place the compass point on C and set its width to the point B.
6. Without changing the compass width, place the compass point on the the point Q and draw an arc across the previously drawn arc. The intersection of these two arcs becomes point R.
7. Using the straightedge, draw a line from point P to R where the arcs intersect.
8. Done. The angle ∠QPR is congruent (equal in measure) to angle ∠CAB.

Try it yourself

Click here for a printable worksheet containing two angle 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

Triangle Centers

Circles, Arcs and Ellipses

Non-Euclidean constructions