Parallel and Perpendicular Lines
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Alternate Exterior Angles
Alternate Interior Angles
Consecutive Exterior Angles
Consecutive Interior Angles
Corresponding AnglesTwo angles that are in the same relative place compared to each of the two lines and the transversal that cuts them. Corresponding angles are congruent if and only if the two lines crossed by the transversal are parallel.
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?
Parallel PostulateEuclid's fifth postulate, and it's quite a tricky one compared to the previous four. It states that if two lines are crossed by a third and both angles on the interior and same side add up to less than the sum of two right angles, the two original lines will eventually intersect on that side. What a mouthful, Euclid. Sheesh.
PerpendicularTwo lines that intersect at exactly 90°, forming four right angles.
PolygonA closed two-dimensional shape that is made of only straight line segments. No curves allowed. Sorry, Beyoncé.
TransversalA line that intersects two other lines, forming a total of eight angles. If the other two lines are parallel (and they usually are), then all these angles are special in some way.