| A | B |
|---|
| line | a one-dimensional figure that extends forever in both directions |
| segment | part of a line, with two endpoints |
| endpoint | a point at the end of a segment or ray |
| ray | a part of a line that has one endpoint and extends forever in the other direction |
| intersect | to cross through the same point |
| perpendicular | two lines are pendicular if they cross at right angles |
| parallel | two lines, segments, or rays that do not cross, no matter how far they extend |
| angle | two rays with the same endpoint |
| side | each of the rays forming an angle |
| vertex | the common endpoint of two rays forming an angle |
| acute angle | an angle smaller than a right angle |
| right angle | an angle like the corner of an index card; measures 90 degrees |
| obtuse angle | an angle greater than a right angle but smaller than a straight angle |
| straight angle | an angle formed by two rays pointing in opposite directions |
| degree | a unit of angle measure; 1/360 of a complete circle |
| complementary angles | two angles whose measures add up to 90 degrees |
| supplementary angles | two angles whose measures add up to 180 degrees |
| protractor | a tool that measures angles |
