How can you divide an angle into 3 equal angles? You may only use a straightedge and a compass to achieve this.

(This means : You have an angle A, you divide Angle A into 3 Angles B,C,D. And B=C=D=A/3)

Note: vohonam clarified that the problem actually only gives you a straightedge, not a ruler.

I notice that you used the word "ruler" instead of the more traditional "straightedge." That is good, because with compass and straightedge alone, it is impossible to trisect most angles. Special angles like 90°, 135°, and 180° can be trisected only because it is possible to independantly construct a 45° or 60° angle.

I have heard of it being done with a marked straightedge. Presumably it is done using line segments of two lengths either of which cannot generate the other.

Posted by TomM on 2002-06-19 10:42:27