• Construct copies of segments and angles
  • Construct segments, perpendicular bisectors of segments, and bisectors of angles
  • Apply construction to problems involving portions of segments and angles

Assignment

  • Three vocabulary definitions
  • p20 10–19, 21–25 (15 problems)

If we’re going to spend all this time looking and figures and shapes, it’ll be helpful to know how to draw them accurately. And we’ll draw these basic constructions without measuring anything, instead using only a compass and a straightedge.

The more complex stuff, like drawing perfect polygons, we might touch on later in the year.

Copying Segments and Angles

The most basic of basic constructions. For copying a line segment, just set the compass to the length of the original, then use it to mark the point for the copy. Here is an animation to help you out.

Copying an angle is a bit more involved. First, you need a place to put the copy, so just a plain line somewhere will do. Then, draw an arc that hits both sides of the original angle. Draw that same arc on the new line.

Finally, on the original angle, set the compass

Bisectors

  1. Perpendicular bisectors
  2. Angle bisector

    If you are interested, Euclidea is a game centered around constructions. You can play in a browser or download it as an app.