26 terms

point

marks a location; has no size

line

extends in both directions forever

plane

a flat surface that extends forever

ray

A part of a line, with one endpoint, that continues without end in one direction

line segment

A part of a line with two endpoints

congruent

Having the same size and shape

intersecting lines

lines that cross at exactly one point

perpendicular lines

Lines that intersect to form right angles

parallel lines

lines that never intersect

angle

A figure formed by two rays with a common endpoint

vertex

The common endpoint of an angle

degree

A unit of measurement of angles

right angle

an angle that measures 90 degrees

acute angle

an angle that measures less than 90 degrees

obtuse angle

An angle that measures more than 90 degrees but less than 180 degrees

straight angle

an angle that measures 180 degrees

vertical angles

A pair of opposite congruent angles formed by intersecting lines; vertical angles are congruent

supplementary angles

Two angles whose sum is 180 degrees

complementary angles

Two angles whose sum is 90 degrees

right triangle

a triangle with one right angle

triangle

a figure with 3 sides and 3 angles; sum of its angles is always 180 degrees

acute triangle

A triangle with 3 acute angles

obtuse triangle

a triangle with one obtuse angle

scalene triangle

a triangle with no congruent sides

isosceles triangle

a triangle with at least two congruent sides

equilateral triangle

A triangle with three congruent sides