Proportion is difficult to estimate and only slightly easier (if more time consuming) to construct. Proportion, however, is suprisingly useful. It is used in art, architechure, nature, and many other places. Proportion is useful in geometry, as well. You can use it to find parts of triangles and other things.

This construction makes a fourth segment in proportion to another three. Some other types of proportion are Geometric Mean, and The Golden Ratio.

The specific proportion that this makes is

a/b = c/x

where "x" is the segment constructed.

For simplicity, the basic ideas of the construction are shown here and not the entire process in step "6". However, it is linked so that if you want, you can look at separate constructions which illustrate how to do it in more detail.

1. Draw a line AB in any direction with length "a".

2. Extend line AB and mark off another segment with length "b".

3. Draw another line starting at A in any direction (except on top of line AB).

4. On this line, draw AD with length "c".

5. Draw BD.

6. Draw a line parallel to BD through C intersecting line AD at E.

DE is equal to "x"

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