| A | B |
|---|
| parallel lines | coplanar lines that do not intersect |
| skew lines | noncoplanar lines |
| a parallel line and plane | line and plan that do not intersect |
| transversal | line that intersects two or more coplanar lines in different points |
| alternate interior angles | two nonadjacent interior angles on opposite sides of a transversal |
| same side interior angles | two interior angles on same sides of a transversal |
| corresponding angles | two angles in a corresponding position relative to two lines |
| triangle | the figure formed by three segments joining three noncollinear points |
| scalene triangle | triangle with no sides congruent |
| isosceles triangle | triangle with at least two sides congruent |
| right triangle | triangle with one right angle |
| obtuse triangle | triangle with one obtuse angle |
| equilateral triangle | triangles with all sides congruent |
| acute triangle | triangle with three acute angles |
| equiangular triangle | triangle with all angles congruent |
| auxiliary line | a line/ray/segment added to a diagram to help in a proof |
| corollary | statement that can be proved easily by applying a theorem |
| polygon | figure formed by coplanar segments such that each segment intersects exactly two other segments one at each endpoint and having no two segments with a common endpoint |
| convex polygon | polygon such that no line containing a side of the polygon contains a point in the interior of the polygon |
| quadrilateral | polygon with four sides |
| pentagon | polygon with five sides |
| hexagon | polygon with six sides |
| octagon | polygon with eight sides |
| decagon | polygon with ten sides |
| nonconvex polygon | polygon such that a line containing a side of the polygon contains a point in the interior of the polygon |
| regular polygon | polygon that is both equiangular and equilateral |
