Creating the rest of the octagon by mirror effect

1. In the Copy window, choose Lines and Mirror. Be sure the option Two Dimensions has been selected.

2. Enter two points that define a vertical axis of symmetry, for example
   (0, 0, 0) and (0, 10, 0).

3. Choose Select and select the two sides of the octagon that have been drawn. Press ESC to conclude the selection. (Figure 19)

4. Repeat the process entering two points that define a horizontal axis of symmetry, for example (0, 0, 0) and (10, 0, 0). This time select the four sides of the octagon (Figure 20)