# Geometry for Elementary School/Copying an angle

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In this chapter, we will show how to copy an angle to other angle . The construction is based on Book I, proposition 23.

## The construction[edit]

- Draw a line between
**A**and**C**and get . - Copy the triangle and get

## Claim[edit]

The angles and are equal.

## Proof[edit]

- The triangles and congruence.
- Therefore the angles of the triangles equal.
- Hence, and are equal.

Note that any two points on the rays can be used to create a triangle.