plane shape A shape in a plane that

plane shape • A shape in a plane that is formed by curves, line segments, or both. These are some plane figures 12. 1

point An exact position or location . point 12. 1

line • A straight path extending in both directions with no endpoints Example: 12. 1

endpoints • Points that are used to show segments of lines. Example: 12. 1

line segment • A part of a line that includes two points, called endpoints, and all the points between them Example: 12. 1

ray • A part of a line, with one endpoint, that is straight and continues in one direction. Example: 12. 1

two-dimensional shape • A shape that lies in a plane; a shape having length and width. Example: 12. 1

closed shape • A shape that begins and ends at the same point. Examples: 12. 1

Open shape • A shape that does not begin and end at the same point. Examples: 12. 1

angle • A figure formed by two rays or line segments that share an endpoint. Example: 12. 2

vertex • The point at which two rays of an angle or two (or more) line segments meet in a plane figure • Example 12. 2

right angle • An angle that forms a square corner Example: 12. 2

acute angle • An angle that has a measure less than a right angle. Example:

obtuse angle • An angle that has a measure greater than a right angle. Example

straight angle • An angle in which two rays point in opposite directions so that they form a line Example:

polygon • A closed plane figure with straight sides that are line segments. Examples: 12. 3

side • a line segment of a polygon Example: This polygon has 4 sides 12. 3

triangle • A polygon with three sides and three angles. Examples: 12. 3

quadrilateral • A polygon with four sides and four angles. Example: 12. 3

pentagon • A polygon with five sides and five angles. Examples: 12. 3

hexagon • A polygon with six sides. Examples: 12. 3

octagon • A polygon with eight sides and eight angles. Examples : 12. 3

Decagon • A polygon with ten sides and ten angles. Example: 12. 3

intersecting lines • lines that cross Example: 12. 4

perpendicular lines • Lines that intersect to form right angles. Example: 12. 4

parallel lines • Lines that never cross; lines that are always the same distance apart. Example: 12. 4

parallelogram • A quadrilateral whose opposite sides are parallel and have the same length. Example :

trapezoid • A quadrilateral with exactly one pair of parallel sides and four angles. Example:

rectangle A quadrilateral with 2 pairs of parallel sides, 2 pairs of equal sides, and 4 right angles. Example: 12. 5

square A quadrilateral with 2 pairs of parallel sides, 4 equal sides, and 4 right angles. Example: 12. 5

rhombus • A quadrilateral with 2 pairs of parallel sides and 4 equal sides and four angles. Example: 12. 5

equilateral triangle • A triangle that has three equal sides and three equal angles. • Examples:

isosceles triangle • A triangle that has two equal sides. Example:

scalene triangle • A triangle in which no sides are equal Example:

right triangle • A triangle with one right angle Example:

obtuse triangle • A triangle that has 1 obtuse angle (an angle greater than a right angle). Example:

acute triangle • A triangle that has three acute angles (angles less than a right angle). Example:

Venn Diagram A diagram that shows relationships among sets of things. 12. 8

diagonal • A line segment that connects two vertices of a polygon that are not next to each other Example:

congruent • Figures that have the same size and shape. Example: