angle

An angle is a figure that is formed by two rays that extend from a common point.

vertex

The vertex of an angle is the point where the two rays forming the angle intersect.

degrees

A degree is a unit of measure of an angle.

right angle

A right angle is an angle that has a measure of exactly 90 degrees.

Acute angle

 An acute angle is an angle that has a measure between 0 and 90 degrees.

 straight angle

A straight angle has a measure of exactly 180 degrees.

obtuse angle

An obtuse angle is an angle that measures between 90 and 180 degrees.

protractor

A protractor is a tool used to measure angles.

complementary angles

Complementary angles are two angles whose sum is 90 degrees.

supplementary angles

Supplementary angles are two angles whose sum is equal to 180 degrees.

transversal

A transversal is a line that intersects two or more lines in the same plane at different points.

congruent angles

Congruent angles are two angles that have the same shape and size.

alternate interior angles

When two parallel lines are cut by a transversal, alternate interior angles are the two angles that lie between the two lines and on opposite sides of a transversal.

alternate exterior angles

When two parallel lines are cut by a transversal, alternate exterior angles are two angles that lie outside of the two lines and on opposite sides of a transversal.

corresponding angles

When two parallel lines are cut by a transversal, corresponding angles are two angles that lie on the same side of the transversal, one angle on the outside of the two lines and one angle on the inside of the two lines.

vertical angles

Two angles are vertical angles if their sides form two pairs of opposite rays.

adjacent angles

Adjacent angles are angles that share a common side and a common vertex and lie on opposite sides of their common side.

triangle

 A triangle has three angles and three sides.

equilateral triangle

An equilateral triangle is a triangle in which all three sides are equal in length. The measure of each interior angle of an equilateral triangle is 60 degrees.

isosceles triangle

An isosceles triangle is a triangle with at least two congruent sides.

scalene triangle

A scalene triangle is a triangle with no sides of equal length.

acute triangle

An acute triangle is a triangle with three acute interior angles.

obtuse triangle

An obtuse triangle is a triangle with one obtuse angle.

right triangle

A right triangle is a triangle that contains a right angle.

quadrilateral

A quadrilateral is a polygon that has four sides.

trapezoid

A trapezoid is a quadrilateral with exactly one pair of parallel sides.

parallelogram

A parallelogram is a quadrilateral in which both pairs of opposite sides are parallel.

rhombus

A rhombus is a parallelogram whose four sides have the same length. The plural form of "rhombus" is "rhombi".

rectangle

A rectangle is a parallelogram with four right angles.

square

A square is a parallelogram with congruent sides and four right angles.

polygon

A polygon is a two-dimensional figure that is formed by three or more segments called sides. Each side of a polygon must intersect exactly two other sides, one at each endpoint. No two sides intersect each other more than once.

diagonal

A diagonal is a line segment that connects any two non-adjacent vertices.

regular polygon

A regular polygon is a polygon whose sides all have the same length and whose angles all have the same measure.

irregular polygon

An irregular polygon is a polygon whose sides are not the same length and whose angles do not have the same measure.

similar polygons

Two polygons are similar when they have the same shape but are not necessarily the same size. The corresponding angles of similar polygons are congruent and the corresponding sides of similar polygons are proportional.

corresponding sides

Corresponding parts of two similar or congruent figures are pairs of sides or angles that are in the same relative position in both figures.

scale factor

A scale factor is a ratio that compares a measurement of a scale model or drawing to the corresponding measurement of an original object. A scale factor is also called a dilation factor.

corresponding angles

When two parallel lines are cut by a transversal, corresponding angles are two angles that lie on the same side of the transversal, one angle on the outside of the two lines and one angle on the inside of the two lines.

indirect measurement

Indirect measurement uses similar triangles and a proportion to measure an object that is not easily measured directly.

congruent polygons

Two figures are congruent if they have the same size and the same shape.

congruent

Same size and same shape