| acute angle |
An angle that measures more than 0° but less than 90°. |
| adjacent angles |
Two angles in the same plane that share a common side and common vertex. |
| area |
The amount of space, or number of square units, inside a closed figure. |
| base |
The side of a triangle from which the height is constructed. |
| base angle |
The angle that is formed by the base and one leg in an isosceles triangle. The base angles are always equal. |
| chord |
A line segment that divides a circle into two segments. |
| circle |
A geometric shape formed by the group of points that are an equal distance from a point, or center. |
| circumference |
The boundary or perimeter around a circle. Circumference measures the distance around a circle. |
| complementary angles |
Two angles whose measurements add up to 90°. |
| consecutive angles |
Angles that occur one right after the other. Consecutive angles are on either end of the same line segment in a polygon. |
| consecutive sides |
Two sides that occur one right after another and that share an endpoint. Consecutive sides connect to form a closed figure in a polygon. |
| degree |
The most commonly used unit of measurement for an angle. The degree symbol is a small circle above and to the right of a number, as in 90°. |
| diameter |
The distance from one edge of the circle to the opposite edge that passes through the center. |
| endpoint |
One of two points on a line segment that signifies where the line segment ends. |
| equiangular |
Having angles that are all equal. |
| equidistant |
Of the same, or equal distance. |
| equilateral triangle |
A triangle with three equal sides and three equal angles. |
| exterior angle |
An angle that lies outside a closed figure or outside parallel lines. |
| geometry |
A section of mathematics that involves the measurements, properties, and relationships of all shapes and sizes of things. |
| height |
A perpendicular line drawn from the highest point in the triangle to the base on the opposite side. |
| interior angle |
An angle that lies inside a closed figure or between parallel lines. |
| isosceles triangle |
A triangle with two equal sides. |
| leg |
One of the two equal sides in an isosceles triangle. |
| line |
A set of numerous points that extend endlessly in two directions. A line is the quickest way to get from one point to another. |
| line segment |
A portion of a line that has a beginning and an end. A line segment can be measured. |
| major segment |
The larger portion of a circle that is cut off by a chord. |
| minor segment |
The smaller portion of a circle that is cut off by a chord. |
| obtuse angle |
An angle that measures more than 90° but less than 180°. |
| opposite sides |
The sides in a quadrilateral that occur opposite from one another. |
| parallel lines |
Lines that do not intersect and do not share any points. Parallel lines are equally distant from each other. |
| parallelogram |
A quadrilateral with opposite parallel sides. |
| perpendicular lines |
The formation of a right angle between two lines. The corner of a piece of paper is formed by perpendicular lines. |
| pi |
A special constant value that relates the diameter of a circle to its circumference. Pi is used to find the circumference and area of a circle and applies for any circle. |
| plane |
A flat surface that extends infinitely in any direction in three dimensions. A plane is represented by a closed four-sided figure. |
| point |
A dot that indicates a definite position or location. A point has no width, depth, or length. |
| point of tangency |
The point at which a tangent touches a circle. |
| polygon |
A closed shape consisting of line segments that has at least three sides. Triangles, quadrilaterals, rectangles, and squares are all types of polygons. |
| protractor |
A tool that can be used to measure or create an angle. |
| quadrilateral |
A polygon with four sides. |
| radii |
The plural term for radius. |
| radius |
The distance from the center to the edge of a circle. |
| ray |
A portion of a line that has only one endpoint and extends infinitely in one direction. The length of a ray cannot be measured. |
| rectangle |
A parallelogram with four right angles. |
| regular polygon |
A type of polygon with sides and angles that are all equal. A stop sign is a regular polygon with eight sides and eight angles. |
| rhombi |
The plural term for rhombus. |
| rhombus |
A parallelogram with equal sides. A rhombus often resembles a diamond. |
| right angle |
An angle formed by two lines that are perpendicular to one another and measures exactly 90°. The corner of a piece of paper is a right angle. |
| scalene triangle |
A triangle with three unequal sides. |
| secant |
A line, line segment, or ray that intersects a circle at two points. |
| square |
A rectangle with four equal sides. |
| straight angle |
An angle that measures 180°. A straight angle resembles a straight line. |
| supplementary angles |
Two angles whose measurements add up to 180°. |
| tangent |
A line, line segment, or ray that touches a circle at exactly one point. |
| transversal line |
A line that crosses two or more lines at different points. |
| triangle |
A polygon with three sides. |
| vertex |
The point where the two sides of an angle intersect. |
| vertex angle |
The angle formed by the two equal legs in an isosceles triangle. The vertex angle is opposite from the base. |
| vertical angles |
Two angles positioned across from each other in the same plane but not next to each other. Vertical angles are formed by intersecting lines and they share the same vertex. |
| vertices |
The plural term for vertex. |