| A | B |
|---|
| parallel lines | lines in the same plane that do not intersect |
| perpendicular lines | two lines that intersect to form a right angle |
| skew lines | lines that do not intersect and are not in the same plane |
| adjacent angles | two angles in the same plane that have a common vertex and a common side but not common interior points |
| vertical angles | two nonadjacent angles formed by two intersecting lines |
| linear angles | a pair of adjacent angles whose noncommon sides are opposite rays. Two adjacent angles whose sum is 180 degrees. |
| complementary angles | two angles whose degree measures have a sum of 90 degrees |
| supplementary angles | two angles whose degree measure have a sum of 180 degrees |
| acute angle | an angle whose degree measure is less than 90 degrees |
| right angle | an angle whose degree measure is exactly 90 degrees |
| obtuse angle | an angle whose degree measure is greater than 90 degrees and less than 180 degrees |
| straight angle | a figure formed by two opposite rays. A straight angle measures exactly 180 degrees |
| counterexample | an example used to show that a given general statement is not always true |
