| Question | Answer |
| THEOREM | a statement that has been proved |
| SUPPLEMENTARY ANGLES | two angles whose measures add to 180 degrees |
| CIRCUMFERENCE | the distance around a circle |
| LINEAR PAIR | two adjacent angles whose noncommon sides form opposite rays |
| COLLINEAR | points that lie on the same line |
| COUNTEREXAMPLE | a case that proves the conjecture wrong |
| ADJACENT ANGLES | two angles in the same plane that have a common side, a common vertex, but no common interior points |
| ANGLE BISECTOR | a ray (or segment) that has an endpoint on the vertex of the angle and that divides the angle into two adjacent, congruent angles |
| SKEW LINES | noncoplanar lines that never intersect |
| CONVERSE | the statement formed by switching the hypothesis and conclusion of a conditional statement |
| RAY | part of a line that consists of a point (initial point) and all the points in one direction |
| AREA | the measure of the region enclosed by a plane figure |
| PERIMETER | the distance around a polygon |
| OPPOSITE RAYS | two rays that are part of the same line, have the same initial point, and go in opposite directions |
| MIDPOINT | the point in the middle of the segment |
| CONJECTURE | the generalization a mathematician makes when using inductive reasoning |
| PERPENDICULAR LINES | coplanar lines that never intersect |
| COMPASS | an instrument used to draw circles |
| VERTICAL ANGLES | two nonadjacent angles formed by intersecting lines |
| POSTULATE or AXIOM | a set of universally accepted statements |
| INDUCTIVE REASONING | the process of observing data, recognizing patterns, and making generalizations from the observations |
| VERTEX | the common endpoint of the two rays that form an angle |
| TRANSVERSAL | line that intersects two or more coplanar lines |
| COMPLEMENTARY ANGLES | two angles whose measures add to 90 degrees |
| COPLANAR | points and lines that lie in the same plane |
| CONCLUSION | the “then” part of a conditional |
| GEOMETRY | the branch of mathematics that is concerned with the properties and relationships of points, lines, angles, curves, surfaces, and solids; it literally means “to measure the earth” |
| ANGLE | two rays that share a common endpoint, provided the two rays do not lie on the same line |
| CONDITIONAL STATEMENT | a statement written in “if-then” form |
| DEDUCTIVE REASONING | the process of demonstrating that if certain statements are accepted as true, then other statements can be shown to follow from them |
| BICONDITIONAL STATEMENT | a statement that contains the phrase “if and only if” |
| LINE SEGMENT | part of a line that consists of two points (endpoints) and all the points between them that lie on the line containing the two points |
| POINT, LINE, AND PLANE | the three undefined terms in geometry |
| HYPOTHESIS | the “if” part of a conditional |
| SEGMENT BISECTOR | a line that passes through the midpoint of a segment |
| PARALLEL LINES | coplanar lines that never intersect |
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