| A | B |
| parallel lines | lines in the same plan that do not intersect |
| skew lines | lines not in the same plane; they do not intersect |
| perpendicular lines | lines that intersect to form right angles |
| complementary angles | the sum of their measures equals 90 |
| supplementary angles | the sum of their measures equals 180 |
| scalene triangle | no sides the same length |
| isosceles triangle | at least two sides the same length |
| equilateral triangle | all three sides the same length |