| A | B |
|---|
| point | An exact location in space. |
| line | An endless collection of points along a straight path. It has no endpoints. |
| line segment | A part of a line having two endpoints. |
| ray | A part of a line that has one endpoint and goes on and on in one direction. |
| plane | An endless flat surface that is named by any three points not on the same line. |
| intersecting lines | Lines that have exactly one point in common. |
| parallel lines | Lines in the same plane that NEVER intersect. |
| perpendicular lines | Two lines that intersect at right angles. |
| angle | Two rays with a common endpoint. |
| acute angle | An angle with a measure LESS than 90 degrees. |
| obtuse angle | An angle with a measure MORE than 90 degrees. |
| right angle | An angle that measures EXACTLY 90 degrees. |
| straight angle | An angle that measures EXACTLY 180 degrees. |
| angle ruler OR protractor | An INSTRUMENT used to measure or draw angles. |
| degree | A UNIT for measuring angles. |
| circle | A closed plane figure. All the points are the same distance from a point called the center. |
| center | The POINT from which all points on a circle are equally distant. |
| chord | A line segment with both endpoints on the circle. |
| circumference | The distance around a circle. |
| diameter | A line segment that passes through the center of a circle and has both endpoints on the circle. |
| radius | A line segment with one endpoint on the circle and the other endpoint at the center. |
| polygon | A closed plane figure with line segments as sides. |
| regular polygon | A polygon with all sides congruent and all angles congruent. |
| triangle | A polygon with three sides. |
| quadrilateral | A polygon with four sides. |
| pentagon | A polygon with five sides. |
| hexagon | A polygon with six sides. |
| septagon OR heptagon | A polygon with seven sides. |
| octagon | A polygon with eight sides. |
| nonagon | A polygon with nine sides. |
| decagon | A polygon with ten sides. |
| acute triangle | A triangle with three acute angles. |
| obtuse triangle | A triangle with one obtuse angle. |
| right triangle | A triangle with one right angle. |
| equilateral triangle | A triangle with all sides and angles equal. |
| isosceles triangle | A triangle with TWO congruent sides. |
| scalene triangle | A triangle that has no congruent sides. |
| parallelogram | A quadrilateral with each pair of opposite sides parallel and congruent. |
| rectangle | A parallelogram with four right angles. |
| rhombus | A parallelogram with all sides congruent. |
| square | A rectangle with all sides congruent. |
| trapezoid | A quadrilateral with only one pair of opposite sides parallel. |
| congruent | Figures that have the same size and shape. |
| transformation | The turning, sliding, or flipping of a plane figure. |
| flip/reflection | A change in position that produces a mirror image of a figure. |
| slide/translation | A change in position that moves a figure up, down, or over. |
| turn/rotation | A change in position that rotates a figure around a point. |
| similar | Figures that have the same shape but no necessarily the same size. |
| symmetry | A figure is symmetric if it can be folded along a line so that the two resulting parts match exactly. |
| line of symmetry | A line that divides a figure, when folded along the line, into two congruent parts. |
