Points, Lines, Angles, and Planes
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AcuteAn adorable little angle. By "little," of course we mean "smaller than 90 degrees in measure."
AdjacentThe conjoined twins of the geometry world. Adjacent angles always share a vertex and a side.
AngleThe corner of empty space between two lines, rays, or segments that share a point. Usually, angles are measured in degrees (and most of them have at least a bachelor's degree).
BisectedSplit in two. We can say that an angle is bisected, a segment is bisected, or that the Dakotas are bisected.
BisectorSomething that splits another thing in half. Like a ray being an angle bisector, or a point bisecting a line segment, or a chainsaw bisecting a zombie.
CollinearUsed to describe points that are all on the same line.
Complementary AnglesTwo wrongs don't make a right, but two complementary angles do. They're two angles that add up to 90° exactly.
CoplanarUsed to describe lines or points that are all on the same plane.
Distance FormulaA formula that calculates distances based on the coordinates we plug into it. It takes the form of this lovely thing: .
LengthThe distance between two endpoints. Can be expressed in units of millimeters, inches, feet, miles, or light-years—they're all lengths.
LineA one-dimensional segment that continues on forever in both directions. Time-consuming to draw, so we use arrows on the ends to symbolize that it never ends.
Line SegmentSometimes just called a "segment." It's a finite piece of line between two endpoints.
MidpointA point that bisects a line segment into two congruent segments. It's the halfway point.
ObtuseAn angle larger than 90° in measure. It has nothing to do with their smarts.
OriginThe point (0, 0) on the x-y graph. In 3D space, it's (0, 0, 0). For any additional dimensions, just add more zeros.
ParallelTwo lines that are on the same plane but never intersect. They're always in sight, but never touch…sort of sad, ain't it?
PerpendicularTwo lines that create a 90° angle when they intersect. Well, actually they create four 90° angles, but who's counting?
PlaneA "slice" of three-dimensional space. It has length and width, but no depth, like a sheet of paper that stretches out forever in all directions.
PointThe smallest object…ever. It has no mass, no length, and no size. It describes only a location.
RayA hybrid of a line and a segment. It has one endpoint, but then goes off forever in the other direction. It's like a ray of sunshine that starts at the sun and then continues on forever.
Right AngleAn angle that's exactly 90°. Naturally, that means any angle that isn't 90° is wrong.
Straight AngleAn angle that measures 180°. The title a straight line gives itself when it wants to seem more impressive.
Supplementary AnglesTwo angles that add up to 180°. It doesn't matter if they're adjacent or on different planets.
Vertical AnglesAngles that are opposite each other resulting from two intersecting lines. Vertical angles are always congruent.