# TRIGONOMETRY GLOSSARY

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Title Description
i, Square Root of -1 The small-case i is reserved for the square-root of a negative one; the square of i is -1.
Identity As opposed to a conditional statement that is sometimes true, an Identity will always be true.
The multiplicative identity is 1; the additive identity is zero.
If-and-Only-If (Iff) A statement that shows a condition both necessary and sufficient for the assertion.
If-Then Statement The classic biconditional statement is often phrased as an If-Then proposition.
Imaginary Number Imaginary Numbers exist, but we do not call them "real."
Incenter The center of a circle inscribed within a polygon.
For a triangle, it is the point of concurrence of the angle bisectors.
Infinite In common language, not countable in any practical manner.
In math, having no bounds or boundary.
Infinite Series Any series of terms whose progression has an unlimited (limitless) number of terms is an Infinite Series.
Infinitesimal Infinitely small is Infinitesimal, so tiny that it occupies no space.
While in human terms anything really small (a molecule) is Infinitesimal, in math the term means approaching zero in size.
Infinity That without bound; limitless.
Initial Side of an Angle In standard position, the Initial Side of an Angle is the ray along the positive x-axis, from the origin.
Inscribed Angle An angle inside a circle with its vertex on the circle is an Inscribed Angle.
Inscribed Circle This term is the same as Incircle, a circle inscribed within a polygon.
Interior Angle Any angle inside a geometric entity, or between geometric lines, is considered an Interior Angle.
Interval The space or region between two defined values is an Interval.
Invariant Constant.
Not changing.
Static.
That which does not vary.
Inverse Cosecant Given a number, this function returns the angle whose cosecant is the given number.
Inverse Cosine Given a number, this function returns the angle whose cosine is the given number.
Inverse Cotangent Given a number, this function returns the angle whose cotangent is the given number.
Inverse Secant Given a number, this function returns the angle whose secant is the given number.
Inverse Sine Given a number, this function returns the angle whose sine is the given number.
Inverse Tangent Given a number, this function returns the angle whose tangent is the given number.
Inverse Trigonometric Function Given a number, this function returns the angle whose trig function is the given number.
Iota The ninth letter of the Greek alphabet, Iota means a very small amount.
Isosceles Triangle A triangle with two congruent sides.

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