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Illustration of a Cartesian coordinate plane. Four points are marked and labeled with their coordinates: (2,3) in green, (−3,1) in red, (−1.5,−2.5) in blue, and the origin (0,0) in purple.

A three dimensional Cartesian coordinate system, with origin O and axis lines X, Y and Z, oriented as shown by the arrows. The tick marks on the axes are one length unit apart. The black dot shows the point with coordinates x = 2, y = 3, and z = 4, or (2,3,4).

Enneagon stellations.svg
Enneagrams shown as sequential stellations
Edges and vertices9
Symmetry groupDihedral (D9)
Internal angle (degrees)100° {9/2}
20° {9/4}

In geometry, an enneagram is a nine-pointed plane figure. It is sometimes called a nonagram.

Complete graphs on n vertices, for n between 1 and 12, are shown below along with the numbers of edges:

K1: 0 K2: 1 K3: 3 K4: 6
Complete graph K1.svg Complete graph K2.svg Complete graph K3.svg 3-simplex graph.svg
K5: 10 K6: 15 K7: 21 K8: 28
4-simplex graph.svg 5-simplex graph.svg 6-simplex graph.svg 7-simplex graph.svg
K9: 36 K10: 45 K11: 55 K12: 66
8-simplex graph.svg 9-simplex graph.svg 10-simplex graph.svg 11-simplex graph.svg