Geometry Help: Segments, Rays, Parallel Lines, and Planes
Discovering, line segments, rays, parallel lines, planes, and more.
Definition: Opposite Rays
Opposite rays are collinear rays with the same endpoint.
Basically, collinear means “on the same line”, so the two rays will look like one line. 
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Definition: Parallel Lines
Parallel lines are coplanar lines, meaning “on the same plane”, that don’t intersect.
The sign for parallelism is a sideways equal sign.
Definition: Skew Lines
Noncoplanar lines. Very simple; noncoplanar, meaning “not within the same plane”.
Lines PS and RY are noncoplanar; therefore, they are skew.
Naming Segments and Rays
Naming Segments
When naming a segment, name both endpoints. The order of the two points written does not matter. The symbol shown above the two points is a short line.
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Naming Rays
When naming a ray, name the endpoint first, then the second point.
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The ray above is called a right ray, because it faces to the right. Left rays, like the one below, face to the left. When naming a ray, the symbol is an arrow pointing to the right. It always points to the right, no matter if it’s a right ray or a left ray. In a left ray, make sure you name the ENDPOINT first. If you do not, and name the points from left to right, IT WILL NOT BE CORRECT!
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One Response to “Geometry Help: Segments, Rays, Parallel Lines, and Planes”
On September 8, 2009 at 1:05 am
aargh.. gave me goosebumps.. reminded me of my grade in this subject..
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