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Definition
The axes of a two-dimensional Cartesian system divide the plane into four infinite regions, called quadrants, each bounded by two half-axes. These are often numbered from 1st to 4th and denoted by Roman numerals: I (where the signs of the (x; y) coordinates are I (+; +), II (−; +), III (−; −), and IV (+; −).
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Vertex (of an angle) The vertex of an angle is the common endpoint of two rays that form the angle.
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Term
| Standard position of an angle |
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Definition
An angle is in standard position if its vertex is located at the origin, and its initial side extends along the positive x-axis. See (Figure). If the angle is measured in a counterclockwise direction from the initial side to the terminal side, the angle is said to be a positive angle.
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| Positive and Negative Angles |
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Definition
The measure of an angle describes the magnitude and direction of the rotation of the ray from its initial position to its terminal position. If the rotation is counterclockwise, the angle has a positive measure. If the rotation is clockwise, the angle has a negative measure.
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The reference angle is the angle that the given angle makes with the x-axis. Regardless of where the angle ends (that is, regardless of the location of the terminal side of the angle), the reference angle measures the closest distance of that terminal side to the x-axis.
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Coterminal angles: are angles in standard position (angles with the initial side on the positive x-axis) that have a common terminal side. For example, the angles 30°, –330° and 390° are all coterminal
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| The amplitude of a periodic variable is a measure of its change in a single period. There are various definitions of amplitude, which are all functions of the magnitude of the differences between the variable's extreme values. |
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