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Math Glossary – Unit 3
Acute angle
A positive angle measuring less than 90 degrees.
Adjacent angles
Two angles that share both a side and a vertex. They always add up to 180
Angle
The union of two rays with a common endpoint, called the vertex.
Arc
A portion of the circumference of a circle.
Complementary angles
Two angles whose sum is 90 degrees.
Congruent
Figures or angles that have the same size and shape.
Degree
A unit of measure of an angle.
Diameter
The line segment joining two points on a circle and passing through the center of
the circle.
Equilateral triangle
A triangle that has three equal sides.
Isosceles triangle
A triangle with at least two equal sides.
Line
A straight set of points that extends into infinity in both directions.
Line segment
Two points on a line, and all the points between those two points.
Obtuse angle
An angle whose measure is greater than 90 degrees.
Parallel
Two lines are parallel if they are in the same plane and never intersect.
Pentagon
A five-sided polygon.
Perimeter
The sum of the lengths of the sides of a polygon.
Perpendicular
Two lines are perpendicular if the angle between them is 90 degrees.
Point
A location in a plane or in space, having no dimensions.
Polygon
A closed plane figure made up of several line segments that are joined together.
Radius
The distance from the center to a point on a circle; the line segment from the
center to a point on a circle.
Reflex angle
Regular polygon
A polygon in which all the angles are equal and all of the sides are equal.
Right angle
An angle whose measure is 90 degrees.
Scalene triangle
A triangle with three unequal sides.
Straight angle
An angle that measures 180 degrees.
Vertex
The point on an angle where the two sides intersect.
Vertical angles
A pair of opposite angles that is formed by intersecting lines.