# How to Copy a Line Segment Using a Compass

The key to copying a given line segment is to open your compass to the length of the segment; then, using that amount of opening, you can mark off another segment of the same length.

Here’s the proof diagram.

This figure shows the solution; refer to it as you work through the following steps.

**Using your straightedge, draw a working line,***l*, with a point*P*anywhere on it.**Put your compass point on point***M*and open it to the length of line*MN*.

The best way to make sure you’ve opened it to just the right amount is to draw a little arc that passes through*N.*In other words, draw arc (*M*,*MN*).**Being careful not to change the amount of the compass’s opening from Step 2, put the compass point on point***P*and construct arc (*P*,*MN*) intersecting line*l*.

You call this point of intersection point *Q,* and you’re done.