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The "∅" symbol is always drawn as a slashed circle, whereas in most typefaces the letter "Ø" is a slashed ellipse. The diameter symbol ( ⌀ ) (Unicode character U+2300) is similar to the lowercase letter ø, and in some typefaces it even uses the same glyph , although in many others the glyphs are subtly distinguishable (normally, the ...
The circle is a highly symmetric shape: every line through the centre forms a line of reflection symmetry, and it has rotational symmetry around the centre for every angle. Its symmetry group is the orthogonal group O(2,R). The group of rotations alone is the circle group T. All circles are similar. [12]
The decimal digits are used for representing numbers through the Hindu–Arabic numeral system. Historically, upper-case letters were used for representing points in geometry, and lower-case letters were used for variables and constants. Letters are used for representing many other types of mathematical object.
In Möbius or inversive geometry, lines are viewed as circles through a point "at infinity" and for any line and any circle, there is a Möbius transformation which maps one to the other. In Möbius geometry, tangency between a line and a circle becomes a special case of tangency between two circles.
The symbol is defined as a circle, with the circular band having a thickness of 10% of the outer diameter of the circle. The inner diagonal line has a thickness of 8% of the outer diameter of the circle (i.e. 80% of the circle's line width). The diagonal is centered in the circle and at a 45-degree angle going from upper left to lower right.
dotted circle: u+25cc circle with vertical fill: u+25cd bullseye: u+25ce black circle: u+25cf circle with left half black: u+25d0 circle with right half black: u+25d1 circle with lower half black: u+25d2 circle with upper half black: u+25d3 circle with upper right quadrant black: u+25d4 circle with all but upper left quadrant black: u+25d5 left ...
A circle, that is, the intersection of a sphere with a secant plane, inverts into a circle, except that if the circle passes through O it inverts into a line. This reduces to the 2D case when the secant plane passes through O , but is a true 3D phenomenon if the secant plane does not pass through O .
Each passes through the corresponding excenter of the triangle, which is the center of similitude for the two circles. Each Soddy line also passes through an analog of the Gergonne point and the Eppstein points. The four Soddy lines concur at the de Longchamps point, the reflection of the orthocenter of the triangle about the circumcenter. [6 ...