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| Geometry | The branch of mathematics that deals with the deduction of the properties, measurement, and relationships of points, lines, angles, and figures in space from their defining conditions by means of certain assumed properties of space. |
| Optical Illusion | Something that deceives by producing a false or misleading impression of reality. |
| Attributes | A quality or characteristic of an object which can be used to identify and classify similar objects. |
| Coordinate geometry | Also called analytic geometry; uses coordinate systems to study the properties of segments, lines, planes, and other figures. |
| Line symmetry | Also called reflection or mirror symmetry; when a figure can be divided into two parts, each of which is the mirror image of the other. |
| Vertical | Upright; at a right angle to the horizon |
| Horizontal | Parallel to the ground; flat or level |
| Rotational symmetry | When a figure coincides with itself after rotating 180 degrees or less, either clockwise or counterclockwise. |
| Midpoint | The point that divides a segment into two congruent segments. |
| Slope | The ratio of rise over run; it represents how steep a line is on a coordinate plane |
| Parallel | Two lines are ______ if they do not intersect and are coplanar. |
| Perpendicular | Two lines are ________ if they intersect to form a right angle. |
| Area | The number of square units contained in the interior of a figure; measured in square units such as square centimeters or square feet. |
| Perimeter | The sum of the lengths of the sides of a polygon. |
| Straightedge | A drafting tool used to sketch lines, segments, and rays. |
| Compass | A drafting tool used for making circles and arcs of a given radius. |
| Bisector | A segment, ray, line, or plane that intersects a segment at its midpoint, or that divides an angle into two congruent angles. |
| Euclid | Known as the "Father of Geometry"; wrote the first textbook on geometry called "The Elements" |
| Similar | Two figures are _________ if corresponding angles are congruent and corresponding sides are proportional. |
| Congruent | For two figures to be _________, they must have all attributes in common. |
