This page shows how to construct a triangle given two sides and the included angle with compass and straightedge or ruler. It works by first copying the angle, then copying the two line segment on to the angle. A third line completes the triangle.
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.
The image below is the final drawing above with the red items added.
|Line segment MN is congruent to AB.
|Drawn with the same compass width. For proof see Copying a line segment
|Line segment ML is congruent to AC.
|Drawn with the same compass width.
|The angle LMN is congruent to the angle A
|Copied using the procedure shown in Copying an angle. See that page for the proof.
|Triangle LNM satisfies the side lengths and angle measure given.