Radian
An angle measure equal to the ratio of arc length to radius, so the measure carries no units.
Reference angle
The acute angle between the terminal side of an angle and the horizontal axis, used with a quadrant sign to produce exact values.
Amplitude
Half the distance between the maximum and minimum of a sinusoidal function.
Phase shift
The horizontal translation of a sinusoidal graph, read only after the coefficient of x has been factored out.
Identity
An equation true for every value in the domain, as opposed to an equation solved for particular values.
Ambiguous case
The SSA configuration, which may describe two triangles, one, or none.
Pole
The origin of the polar coordinate system, from which distance is measured.
Modulus
The distance of a complex number from the origin of the complex plane.
Argument
The direction angle of a complex number measured from the positive real axis.
Hole
A point missing from a rational graph because a factor cancels from numerator and denominator.
Extraneous solution
A value produced by valid algebra that the original equation cannot accept, usually because of a domain restriction.
Indeterminate form
An expression such as 0/0 whose value cannot be decided without rewriting the expression.
Removable discontinuity
A break where the limit exists and finite, so redefining a single value would restore continuity.
Instantaneous rate of change
The limit of an average rate of change as the interval shrinks toward a single point.