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If the polar line of C with respect to a point Q is a line L, then Q is said to be a pole of L. A given line has (n−1) 2 poles (counting multiplicities etc.) where n is the degree of C. To see this, pick two points P and Q on L. The locus of points whose polar lines pass through P is the first polar of P and this is a curve of degree n−1.
In polar coordinates, the polar tangential angle is defined as the angle between the tangent line to the curve at the given point and ray from the origin to the point. [6] If ψ denotes the polar tangential angle, then ψ = φ − θ , where φ is as above and θ is, as usual, the polar angle.
The equation defining a plane curve expressed in polar coordinates is known as a polar equation. In many cases, such an equation can simply be specified by defining r as a function of φ . The resulting curve then consists of points of the form ( r ( φ ), φ ) and can be regarded as the graph of the polar function r .
If a point P moves along a line l, its polar p rotates about the pole L of the line l. If two tangent lines can be drawn from a pole to the conic section, then its polar passes through both tangent points. If a point lies on the conic section, its polar is the tangent through this point to the conic section. If a point P lies on its own polar ...
The polar angle is denoted by [,]: it is the angle between the z-axis and the radial vector connecting the origin to the point in question. The azimuthal angle is denoted by φ ∈ [ 0 , 2 π ] {\displaystyle \varphi \in [0,2\pi ]} : it is the angle between the x -axis and the projection of the radial vector onto the xy -plane.
The angle φ is the angle of inclination of the tangent line or the tangential angle. In geometry, the subtangent and related terms are certain line segments defined using the line tangent to a curve at a given point and the coordinate axes. The terms are somewhat archaic today but were in common use until the early part of the 20th century.
Let Xx + Yy + Zz = 0 be the equation of a line, with (X, Y, Z) being designated its line coordinates in a dual projective plane. The condition that the line is tangent to the curve can be expressed in the form F(X, Y, Z) = 0 which is the tangential equation of the curve. At a point (p, q, r) on the curve, the tangent is given by
If the point p lies on the conic Q, the polar line of p is the tangent line to Q at p. The equation, in homogeneous coordinates, of the polar line of the point p with respect to the non-degenerate conic Q is given by = Just as p uniquely determines its polar line (with respect to a given conic), so each line determines a unique pole p.