# How to Construct an Angle of Fixed Measure

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Occasionally you may want to create an angle of fixed measure — for example, an angle that measures exactly 33°. While you could create an angle by measuring three points and dragging them until they form an angle of 33°, this angle would not be constructed to be fixed at 33°. 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. | Use the Point tool to to construct two points, A and B, in your sketch.

2. | Select point A and choose Transform | Mark Center. Point A is marked as the center of future rotations and dilations.

3. | Select point B and choose Transform | Rotate.

4. | In the dialog box, enter the fixed angle by which you want to rotate. Click the Rotate button to confirm your choices.

5. | 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 to B and to B' to incorporate the fixed angle into your sketch.

See also:

How to Construct a Segment of Fixed Length

How to Construct Congruent Angles