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| Essentially, a point is a zero dimensional(no width length or height) description of a location in space. |
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| 1 dimensional(have only length but not height or width) object that extends infinitely in both directions. |
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| A line segment is a section of a line that has two endpoints. |
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| A section of a line that has one endpoint and goes in forever in the other direction. |
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| Two rays with the same endpoint form an angle. Each ray is a side of the angle, and the commonendpoint is the angle's vertex. |
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| A plane is a two dimensional object(has only length and width but no height) which goes on infinitely in all directions. |
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| 3D space can be considered the opposite of a point in that it has width, height, and length and extends inifintely in every direction -- all of space. |
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| Collinear points are points which lie on the same line. |
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| A group of points that lie in the same plane are coplanar. Any two or three points are always coplanar. Four or more points might or might not be coplanar. |
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| Parallel lines, segments, or rays |
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Definition
| Lines that run in the same direction and never cross are called parallel. Segments and rays are parallel if the lines that contain them are parallel. |
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| Perpendicular lines, segments, or rays |
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| Lines, segments, or rays that intersect at right angles(90° angles) are perpendicular. |
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| Oblique lines, segments, or rays |
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| Lines or segments or rays that intersect at any angles other than 90° are called oblique. |
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| Skew lines, segments, or rays |
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| Lines that don't lie in the same plane are called skew lines -- skew simply means non-coplanar. In other words, skew lines are lines that are neither parallel nor intersecting(i.e. coplanar lines). |
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| Parallel planes are planes that never cross. Think of the flat ceiling and floor of a room as parallel planes. |
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| Planes that cross or intersect. When planes intersect the place where they cross forms a line. Think of the floor and wall of a room as intersecting planes and where the floor meets the wall is the line of intersection of the two planes. |
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| An acute angle is less than 90º. |
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| A right angle is a 90° angle. |
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| An obtuse angle has a measure greater than 90°. |
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| A straight angle has a measure of 180°; it looks like a line with a point on it. |
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| A reflex angle has a measure of more than 180°. Basically, a reflex angle is just the other side of an ordinary angle. |
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| Adjacent angles are neighboring angles that have the same vertex and that share a side; also, neither angle can be inside the other. |
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| Two amgles that add up to 90° are complementary. |
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| Two angles that add up to 180° are supplementary. |
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| When intersecting lines form an X, the angles on the opposite sides of the X are called vertical angles. Two vertical angles are always the same size as each other. |
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| Congruent segments are segments with the same length. |
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| The basic unit od measure for angles is teh degree. One degree is 1/360 of a circle, or 1/360 of one complete rotation. |
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| Congruent angles are angles with the same degree measure. |
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| A point, segment, ray or line that divides a segment into two congruent segments bisects the segment. |
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| The point where a segment is bisected is called the midpoint of the segment; the midpoint cuts the segment into two congruent parts. |
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Two things (points, segments, rays, lines, or any combination of these) that divide a segment into three congruent segments trisects the segment. The points of trisection are called the trisection points of the segment.
Note: If a side of a triangle is trisected by rays from the opposite vertex, the vertex angle can't be trisected. The vertex angle may look like it is trisected but this is not possible. |
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| A ray that cuts an angle into two congruent angles bisects the angle. The ray is called the angle bisector. |
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Two rays that divide an angle into three congruent angles trisect the angle. These rays are called angle trisections.
Note: When rays trisect an angle of a triangle, the opposite side of the triangle is never trisected by these rays. |
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