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To determine the shape of Z D, fix two distinct circles C 0 and C ∞, not necessarily tangent to D. These two circles determine a pencil, meaning a line L in the P 3 of circles. If the equations of C 0 and C ∞ are f and g, respectively, then the points on L correspond to the circles whose equations are Sf + Tg, where [S : T] is a point of P 1.
A circle is tangent to a point if it passes through the point, and tangent to a line if they intersect at a single point P or if the line is perpendicular to a radius drawn from the circle's center to P. Circles tangent to two given points must lie on the perpendicular bisector. Circles tangent to two given lines must lie on the angle bisector.
For two circles, there are generally four distinct lines that are tangent to both – if the two circles are outside each other – but in degenerate cases there may be any number between zero and four bitangent lines; these are addressed below. For two of these, the external tangent lines, the circles fall on the same side of the line; for the ...
In geometry, tangent circles (also known as kissing circles) are circles in a common plane that intersect in a single point. There are two types of tangency : internal and external. Many problems and constructions in geometry are related to tangent circles; such problems often have real-life applications such as trilateration and maximizing the ...
The method hinges on the observation that the radius of a circle is always normal to the circle itself. With this in mind Descartes would construct a circle that was tangent to a given curve. He could then use the radius at the point of intersection to find the slope of a normal line, and from this one can easily find the slope of a tangent line.
All tangent circles to the given circles can be found by varying line . Positions of the centers Circles tangent to two circles. If is the center and the radius of the circle, that is tangent to the given circles at the points ,, then:
In case of = the circles have one point in common and the radical line is a common tangent. Any general case as written above can be transformed by a shift and a rotation into the special case. The intersection of two disks (the interiors of the two circles) forms a shape called a lens.
If two tangent lines can be drawn from a pole to the circle, then its polar passes through both tangent points. If a point lies on the circle, its polar is the tangent through this point. If a point P lies on its own polar line, then P is on the circle. Each line has exactly one pole.