A–F
 AA similarity theorem
Two triangles are similar if they have two corresponding angles that are congruent.
 absolute value
A number’s distance from zero on the number line.
The symbol
means the absolute value of . Recall that distance is always positive.
The diagram shows that
and .  absolute value function
A function that contains an algebraic expression within absolute value symbols. The absolute value parent function, written as:
 adjacent
 adjacent angles
Two nonoverlapping angles with a common vertex and one common side.
and are adjacent angles:  alternate exterior angles
A pair of angles formed by a transversal intersecting two lines. The angles lie outside of the two lines and are on opposite sides of the transversal.
See angles made by a transversal.
 alternate interior angles
A pair of angles formed by a transversal intersecting two lines. The angles lie between the two lines and are on opposite sides of the transversal.
See also angles made by a transversal.
 altitude

Altitude of a triangle:
A perpendicular segment from a vertex to the line containing the base.
Altitude of a solid:
A perpendicular segment from a vertex to the plane containing the base.
 angle
Two rays that share a common endpoint called the vertex of the angle.
 angle bisector
A ray that has its endpoint at the vertex of the angle and divides the angle into two congruent angles.
 angle of depression/angle of elevation

Angle of depression: the angle formed by a horizontal line and the line of sight of a viewer looking down. Sometimes called the angle of decline.
Angle of elevation: the angle formed by a horizontal line and the line of sight of a viewer looking up. Sometimes called the angle of incline.
 angles associated with circles: central angle, inscribed angle, circumscribed angle

Central angle: An angle whose vertex is at the center of a circle and whose sides pass through a pair of points on the circle.
Inscribed angle: An angle formed when two secant lines, or a secant and tangent line, intersect at a point on a circle.
Circumscribed angle: The angle made by two intersecting tangent lines to a circle.
 angles made by a transversal
 arc length
The distance along the arc of a circle. Part of the circumference.
Equation for finding arc length:
Where
is the radius and is the central angle in radians.  arc of a circle, intercepted arc

Arc: A portion of a circle.
Intercepted arc: The portion of a circle that lies between two lines, rays, or line segments that intersect the circle.
 asymptote

A line that a graph approaches, but does not reach. A graph will never touch a vertical asymptote, but it might cross a horizontal or an oblique (also called slant) asymptote.
Horizontal and oblique asymptotes indicate the general behavior of the ends of a graph in both positive and negative directions. If a rational function has a horizontal asymptote, it will not have an oblique asymptote.
Oblique asymptotes only occur when the numerator of
has a degree that is one higher than the degree of the denominator.