POINT A point in geometry is not really anything but some location or position in space. It has no width, length or depth. A point or dot on a piece of paper has some size to it but in geometry there is no size to it. An intersection of two lines could establish a point. LINE: For geometric purposes we will define a line as an infinite straight line extending in two directions. A line has length but no width nor thickness. Let me define this for you. When we draw a line with a pen it has width because we can see it and you could measure it. It is the same width as the tip on the pen. No matter how thin of a pen you are using it still has some dimension to it. But in geometry this line would actually be invisible to our eyes because it is defined as only having length (no thickness nor width. Through two given points one and only one straight line can be drawn. LINE SEGMENT: A section of line between two end points. This is also the shortest distance between two points. In sheet metal line segments are what we always work with. RAY: Portion of line bound in one direction by an end point and extending in the other direction indefinitely. PERPENDICULAR LINES: Lines which intersect at right angles.(90 degrees) PARALLEL LINES: In a plane, lines which cannot meet, however far they may extend. The line, line segment and ray below are all parallel to each other. LINE RAY LINE SEGMENT Back to:
A practical use for a ray in sheet metal development could be  extending the outer surfaces of an acute angle to where they intersect (apex)
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