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Limacon
A polar equation of the form r = a + b sin(θ) or r = a + b cos(θ), where a, b≠ 0.
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Logarithmic Spiral
A polar equation of the form r = abθ.
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Orientation
The direction of a plane curve as the parameter increases.
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Parameter
A third variable (often time) which determines the values of x and y in parametric equations.
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Parametric Equations
Two equations of the form x = f (t) and y = g(t), which specify the location of a point according to the variable t.
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Plane Curve
The set of all points (f (t), g(t)), where x = f (t) and y = g(t) are parametric equations.
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Polar Axis
The ray whose endpoint is the pole and which is the initial side of any angle measure in the polar plane.
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Polar Coordinate System
The system in which a point in the plane is specified according to an ordered pair (r, θ) in which r is a length and θ is an angle. The length r refers to the distance from the point to a fixed origin, called the pole. The angle θ is the angle whose initial side is a fixed ray (the polar axis) and whose terminal side contains the point. Under these circumstances, the point (r, θ) is expressed in polar coordinates.
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Pole
The fixed point in the polar coordinate system from which every point is r units away.
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Rectangular Coordinate System
The coordinate system in which every point is specified by exactly one ordered pair (x, y). Here x is the distance between the point and a fixed line (the y-axis) and y is the distance between the point and a line fixed perpendicular to the other line (this line is the x-axis). The perpendicular lines are the axes, and the point (x, y) is expressed in rectangular coordinates.
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Rose Curve
A polar equation of the form r = a sin(nθ) or r = a cos(nθ), where n is an integer.
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Spiral of Archimedes
A polar equation of the form r = aθ + b.
