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Encyclopedia > Straightedge

A straightedge is a tool similar to a ruler, but without markings. A variety of rulers A 2 metre carpenters rule Retractable flexible rule A ruler or rule is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. ...

## Compass-and-straightedge construction

An idealized straightedge is used in compass-and-straightedge constructions in plane geometry. It may be used: Creating a regular hexagon with a ruler and compass Construction of a regular pentagon Compass and straightedge or ruler-and-compass construction is the construction of lengths or angles using only an idealized ruler and compass. ... Euclid Euclidean geometry is a mathematical system attributed to the Greek mathematician [[Euclid]] of Alexandria. ...

• Given two points, to draw the line connecting them.
• Given a point and a circle, to draw either tangent.
• Given two circles, to draw any of their common tangents.

It may not be marked or used together with the compass so as to transfer the length of one segment to another. a compass In drafting, a compass (or pair of compasses) is an instrument]] used by mathematicians and craftsmen in for drawing or inscribing a circle or arc. ...

It is possible to do all compass and straightedge constructions without the straightedge. That is, it is possible, using only a compass, to find the intersection of two lines given two points on each, and to find the tangent points to circles. It is not, however, possible to do all constructions using only a straightedge. It is possible to do them with straightedge alone given one circle and its center.

## References

• Wayne R. Moore, Foundations of Mechanical Accuracy, Moore Special Tool Company, Bridgeport, CT (1970)

Results from FactBites:

 Straightedge - definition of Straightedge in Encyclopedia (277 words) A straightedge is a tool similar to a ruler, but without markings. It may not be marked or used together with the compass so as to transfer the length of one segment to another. Making a practical straightedge without access to a pre-existing straightedge or modern machine tools is an interesting problem in mechanical engineering.
 StraightEdge (1778 words) Straightedgers can be identified at rock concerts by a fl ``X'' marked on the back of their hands. As a social movement straightedge appears to be a labyrinth of false perceptions. Brummel, 26, says he got involved in straightedge as a teenager because he thought it was cool to chose a positive lifestyle.
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