How To Construct an Angle of Fixed Measure

How To . . . Construct an Angle of Fixed Measure

Occasionally you may wish to create an angle of fixed measure—for example, an angle that measures exactly 33º. While you could create an angle by measuring three points and dragging them until they form an angle of 33º, this angle would not be constructed to be fixed at 33º. That is, dragging it again would change it from its current magnitude to some other magnitude.

To fix an angle in Sketchpad, you need to construct the angle in such a way that dragging cannot change its magnitude. For an arbitrary angle, the easiest way to do this is with the Transform menu.

1. Place two points, A and B, in your sketch.

2. Select point A and choose Mark Center from the Transform menu. Point A becomes marked as the center of future rotations and dilations.

3. Select point B and choose Rotate. In the dialog box, enter the fixed angle by which you wish to rotate.

4. Sketchpad constructs point B' as the rotated image of B by your requested angle. Even if you drag A, B, or B', Sketchpad will maintain this angle’s magnitude, because you’ve defined B' to be the rotated image of B by this angle.

You can now construct rays or segments connecting A, B, and B' to incorporate the fixed angle into your sketch.