compass

To divide a given line segment into a given number of equal parts.
Given:  Line segment AB
Required:  To divide segment AB into 3 equal parts.
Procedure:

divide a line into equal parts

  Use the straightedge tool and draw line AX forming any convenient angle with AB.
  Place and label any point C on AX.
  Use the segment command under the construct menu and construct segment AC.
  Use the circle by center + radius command under the construct menu to construct a circle with center at C and radius congruent to segment AC.  
  Label the intersection of that circle and line AX point D, and repeat the above with D as center.
  Label the next intersection point E.  (repeat as many times as needed to generate the number of equal segments wanted.)
  Use the segment command under the construct menu to construct segment EB.
   Through points C and D draw lines parallel to EB, label the intersections with AB points F and G respectively.(help) (Or use the parallel line command under the construct menu.)
  F and G divide AB into 3 equal parts. 
Proof:
  Since AX is divided into 3 equal parts , AB is divided into 3 equal parts.    (If 3 or more parallels intercept equal segments on one transversal, they intercept equal segments on every transversal)
               
Sketch:   On the sketch below, dark blue circles were used to lay off the equal segments on AX.  Red and green circles constructed the congruent angles.  If you change the length of segment AB is it still divided into equal parts?
 
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divide line segment into given number of parts

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