These are geometry terms you likely saw in middle-school, but might have forgotten since then. Knowing these will make learning the new material easier, even if some might not come up until later in the course.
And here is the PDF version that was given out during class.
The Basics
| Term |
Definition |
| Point |
An exact location with no size or shape. |
| Line |
A straight path that goes on forever in both directions. |
| Line Segment |
A part of a line with two endpoints. |
| Ray |
A part of a line that starts at one point and goes on forever in one direction. |
| Plane |
A flat surface that extends forever in all directions. |
| Angle |
A figure formed by two rays that share an endpoint. |
Angles and Lines
| Term |
Definition |
| Acute Angle |
An angle smaller than 90°. |
| Right Angle |
An angle that measures exactly 90°. |
| Obtuse Angle |
An angle greater than 90° but less than 180°. |
| Parallel Lines |
Lines that never intersect and stay the same distance apart. |
| Perpendicular Lines |
Lines that intersect to form right angles. |
| Complementary Angles |
Two angles whose measures add up to 90°. |
| Supplementary Angles |
Two angles whose measures add up to 180°. |
Polygons
| Term |
Definition |
| Polygon |
A closed figure formed by three or more line segments (sides). |
| Triangle |
A polygon with three sides. |
| Quadrilateral |
A polygon with four sides. |
| Rectangle |
A quadrilateral with four right angles. |
| Square |
A rectangle with four equal sides. |
| Parallelogram |
A quadrilateral with two pairs of parallel sides. |
| Trapezoid |
A quadrilateral with at least one pair of parallel sides. |
Circles
| Term |
Definition |
| Circle |
A set of points that are all the same distance from a center point. |
| Radius |
A segment from the center of a circle to the circle. |
| Diameter |
A segment through the center of a circle with endpoints on the circle. |
| Circumference |
The distance around a circle. |
Measurement
| Term |
Definition |
| Perimeter |
The distance around a polygon. |
| Area |
The amount of space inside a two-dimensional figure. |
| Volume |
The amount of space inside a three-dimensional figure. |
Coordinate Plane
| Term |
Definition |
| Coordinate Plane |
A grid formed by the $x$-axis and $y$-axis. |
| $x$-axis |
The horizontal axis on a coordinate plane. |
| $y$-axis |
The vertical axis on a coordinate plane. |
| Origin |
The point $(0, 0)$ and where the $x$- and $y$-axis intersect. |
| Ordered Pair |
A pair of numbers that tell a point’s location on a coordinate plane. |
| Term |
Definition |
| Transformation |
A function (rule) that moves or changes a figure in some way. |
| Translation |
A transformation that slides a figure without turning or flipping it. |
| Reflection |
A transformation that flips a figure across a line. |
| Rotation |
A transformation that turns a figure around a point. |
| Dilation |
A transformation that makes a figure larger or smaller while keeping its shape. |
Miscellaneous
| Term |
Definition |
| Congruent Figures |
Figures that have the same size and shape. |
| Similar Figures |
Figures that have the same shape but may have different sizes. |
| Scale Factor |
The number used to enlarge or reduce a figure. |
| Symmetry |
When a figure can be divided into matching halves. |
| Pythagorean Theorem |
A rule for finding side lengths in right triangles: $a^2+b^2=c^2$. |